earth science 805 words

  1. ablation
    the erosive process that reduces the size of glaciers
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  2. abnormal
    not normal; not typical or usual or regular or conforming to a norm
    Drought= Abnormal dry weather for a specific area that is sufficiently prolonged for the lack of water to cause serious hydrological imbalance.
  3. abrasion
    erosion by friction
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  4. abrupt
    exceedingly sudden and unexpected
    The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. see Key bed
    Crevasse=A fracture or crack in the upper 40 to 50 meters of a glacier.
  5. absolute
    perfect or complete or pure
    Absolute age=Time measured in years.
  6. absolute magnitude
    (astronomy) the magnitude that a star would have if it were viewed from a distance of 10 parsecs (32.62 light years) from the earth
    Absolute magnitude=The brightness that a star would appear to have if it were 32 light-years (10 parsecs) away.
  7. absolute zero
    (cryogenics) the lowest temperature theoretically attainable (at which the kinetic energy of atoms and molecules is minimal); 0 Kelvin or -273.15 centigrade or -459.67 Fahrenheit
    Absolute Zero=Considered to be the point at which theoretically no molecular activity exists or the temperature at which the volume of a perfect gas vanishes.
  8. absorb
    suck or take up or in
    Absorption nebula=A cold nebula that absorbs light.
  9. absorption spectrum
    the spectrum of electromagnetic radiation that has passed through a medium that absorbed radiation of certain wavelengths
    Absorption spectrum=See "spectrum."
  10. abundant
    present in great quantity
    Eutrophic lake=A lake characterized by abundant dissolved nitrates, phosphates, and other plant nutrients and by a seasonal deficiency of oxygen in bottom water.
  11. abyssal
    relating to ocean depths from 2000 to 5000 meters
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  12. accessory
    a supplementary component that improves capability
    Andesite minerals commonly include plagioclase and hornblende, with lesser amounts of mica, pyroxene, and various accessory minerals.
  13. accompanying
    following or accompanying as a consequence
    Cyclone=A low pressure region with its accompanying surface wind.
  14. accretion
    an increase by natural growth or addition
    Accretion=Accumulation of dust and gas into larger bodies.
  15. accumulate
    get or gather together
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  16. accumulated
    periodically accumulated over time
    Earthquake=A sudden motion or trembling of the Earth caused by the abrupt release of slowly accumulated elastic energy in rocks.
  17. accumulation
    the act of accumulating
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  18. acid
    any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt
    Acid precipitation=A condition in which natural precipitation becomes acidic after reacting with air pollutants.
  19. acid rain
    rain containing acids that form in the atmosphere when industrial gas emissions (especially sulfur dioxide and nitrogen oxides) combine with water
    (Often called " acid rain.")
  20. acidic
    being or containing an acid; of a solution having an excess of hydrogen atoms (having a pH of less than 7)
    Acid precipitation=A condition in which natural precipitation becomes acidic after reacting with air pollutants.
  21. action
    something done (usually as opposed to something said)
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  22. active
    characterized by energetic activity
    Active continental margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: Andean margin)
    Active volcano=A volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
  23. adiabatic
    occurring without loss or gain of heat
    Adiabatic rate=The rate of temperature change in the atmosphere due to the raising or lowering of an air mass.
  24. adjacent
    having a common boundary or edge; abutting; touching
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  25. adjustment
    the act of making something different (as e.g. the size of a garment)
    Asthenosphere=The shell within the earth, some tens of kilometers below the surface and of undefined thickness, which is a shell of weakness where plastic movements take place to permit pressure adjustments.
  26. advection
    (meteorology) the horizontal transfer of heat or other atmospheric properties
    Advection fog=Fog that forms when warm moist air from the sea blows onto cooler land, where the air cools and water vapor condenses at ground level.
  27. aerosol
    a cloud of solid or liquid particles in a gas
    Aerosol=Any small particle that is larger than a molecule and suspended in air.
  28. agent
    a representative who acts on behalf of other persons or organizations
    Deposition=The laying-down of rock-forming materials by any natural agent.
  29. aggregate
    a sum total of many heterogenous things taken together
    An aggregate of cloud droplets forms a visible cloud.
  30. air mass
    a large body of air with uniform characteristics horizontally
    Adiabatic rate=The rate of temperature change in the atmosphere due to the raising or lowering of an air mass.
  31. albedo
    the ratio of reflected to incident light
    Albedo=Reflectivity of an object; ratio of reflected light to incident light.
  32. alloy
    a mixture containing two or more metallic elements or metallic and nonmetallic elements usually fused together or dissolving into each other when molten
    Control rod=A column of neutron-absorbing alloys that are spaced among fuel rods to fine-tune nuclear fission in a reactor.
  33. alluvial
    of or relating to alluvium
    Alluvial fan=A fan-like accumulation of sediment created where a steep stream slows down rapidly as it reaches a relatively flat valley floor.
  34. alluvial fan
    a fan-shaped deposit where a fast flowing stream flattens out
    Alluvial fan=A fan-like accumulation of sediment created where a steep stream slows down rapidly as it reaches a relatively flat valley floor.
  35. alluvium
    clay or silt or gravel carried by rushing streams and deposited where the stream slows down
    Alluvium=A general term for clay, silt, sand, gravel or similar unconsolidated material deposited by a stream or other body of running water.
  36. alpha
    the 1st letter of the Greek alphabet
    Alpha Centauri=The closest bright star to our solar system.
  37. Alpha Centauri
    brightest star in Centaurus; second nearest star to the sun
    Alpha Centauri=The closest bright star to our solar system.
  38. alternate
    go back and forth; swing back and forth between two states or conditions
    Composite cone=A volcano that consists of alternate layers of unconsolidated pyroclastic material and lava flows. (syn: stratovolcano)
    Composite Volcano=A steep volcanic cone built by both lava flows and pyroclastic eruptions.
  39. alternative
    one of a number of things from which only one can be chosen
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  40. alternative energy
    energy derived from sources that do not use up natural resources or harm the environment
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  41. altitude
    elevation especially above sea level or above the earth's surface
    Altimeter=An instrument used to determine the altitude of an object with respect to a fixed level.
  42. altostratus
    a stratus cloud at an intermediate altitude of 2 or 3 miles
    E.g., Altostratus.
  43. aluminum
    a silvery ductile metallic element found primarily in bauxite
    Bauxite=A gray, yellow, or reddish brown rock composed of a mixture of aluminum oxides and hydroxides.
  44. amplify
    increase the volume of
    This movement is amplified by a spring or gear mechanism to indicate changes in air pressure on a scale or recording chart.
  45. anaerobic
    not aerobic
    Anaerobic=Without oxygen; anaerobic bacteria are bacteria that live without oxygen.
  46. analysis
    the abstract separation of a whole into its constituent parts in order to study the parts and their relations
    Cost benefit analysis=A system of analysis that attempts to weigh the cost of an act or policy, such as pollution control, directly against the economic benefits.
  47. anemometer
    a gauge for recording the speed and direction of wind
    Anemometer=an instrument that measures wind speed
    Aneriod Barometer=A barometer whose pressure sensor consists of an aneroid capsule, a thin, hollow disk partially evacuated and sealed.
  48. aneroid
    containing no liquid or actuated without the use of liquid
    Anemometer=an instrument that measures wind speed
    Aneriod Barometer=A barometer whose pressure sensor consists of an aneroid capsule, a thin, hollow disk partially evacuated and sealed.
  49. angular
    having angles or an angular shape
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  50. anion
    a negatively charged ion
    Anion=An ion that has a negative charge.
  51. antecedent
    a preceding occurrence or cause or event
    Antecedent stream=A stream that was established before local uplift started and cut its channel at the same rate the land wasrising.
  52. anticlinal
    sloping downward away from a common crest
    Dome=A circular or elliptical anticlinal structure.
  53. anticyclone
    (meteorology) winds spiraling outward from a high pressure center; circling clockwise in the northern hemisphere and counterclockwise in the southern
    Anticline=A fold in rock that resembles an arch; the fold is convex upward and the oldest rocks are in the middle Anticyclone: An area of high pressure, also called a High, around which the winds circulate in a clockwise direction in the Northern Hemisphere (and counterclockwise in the Southern Hemisphere).
  54. anticyclonic
    of or relating to or characteristic of the atmosphere around a high pressure center
    Anticyclonic=The wind circulation pattern in Highs, or anticyclones, that has a sense of rotation opposite to that of cyclones and the Earth's rotation.
  55. anvil
    a heavy block of iron or steel on which hot metals are shaped by hammering
    The base of cumulus clouds is generally found from 500 to 3000 meters Large cumulonimbus clouds may extend to over 18,000 meters and be topped with anvil-shaped ice clouds.
  56. aphelion
    apoapsis in solar orbit; the point in the orbit of a planet or comet that is at the greatest distance from the sun
    Aphelion =The point in its orbit where a planet is farthest from the Sun.
    Apogee =The point in orbit farthest from the Earth.
  57. apogee
    apoapsis in Earth orbit; the point in its orbit where a satellite is at the greatest distance from the Earth
    Aphelion =The point in its orbit where a planet is farthest from the Sun.
    Apogee =The point in orbit farthest from the Earth.
  58. apparent
    clearly revealed to the mind or the senses or judgment
    Apparent magnitude=The brightness of a star as seen from Earth.
  59. approximately
    (of quantities) imprecise but fairly close to correct
    Air mass=A large body of air that has approximately the same temperature and humidity throughout.
  60. aquifer
    underground bed or layer yielding ground water for wells and springs etc
    Aquifer=A body of rock that contains significant quantities of water that can be tapped by wells or springs.
  61. area
    the extent of a 2-dimensional surface enclosed within a boundary
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  62. argon
    a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere
    Argon (A) at 0.93%; and Carbon Dioxide (CO2) 0.033%.
  63. array
    an impressive display
    Crystal=A solid element or compound whose atoms are arranged in a regular, orderly, periodically repeated array.
  64. artesian
    (of water) rising to the surface under internal hydrostatic pressure
    Artesian aquifer=An inclined aquifer that is bounded top and bottom by layers of impermeable rock so the water is under pressure.
  65. artificial
    contrived by art rather than nature
    Artificial channel=Any channel dredged to modify the natural channel or to alter the course of a stream.
  66. assign
    select something or someone for a specific purpose
    Absolute dating=A technique that geologists use to assign specific dates to rock formations and geologic events.
  67. asteroid
    any of numerous small celestial bodies composed of rock and metal that move around the sun (mainly between the orbits of Mars and Jupiter)
    Asteroid=A rocky space object that can be from a few hundred feet to several hundred km wide.
  68. asthenosphere
    the lower layer of the crust
    Asthenosphere=The shell within the earth, some tens of kilometers below the surface and of undefined thickness, which is a shell of weakness where plastic movements take place to permit pressure adjustments.
  69. astronomer
    a physicist who studies astronomy
    Constellation=One of 88 groups of stars that astronomers refer to for convenience in referring to the positions of objects in the night sky.
  70. astronomical
    relating or belonging to the science of astronomy
    Astronomical unit=(AU) The average distance from the Earth to the Sun; 1 AU is 149,597,870 kilometers (92,960,116 miles).
  71. astronomy
    the branch of physics that studies celestial bodies and the universe as a whole
    Astronomy=Astronomy is the study of everything that lies beyond the Earth's atmosphere.
  72. atmosphere
    the envelope of gases surrounding any celestial body
    Adiabatic rate=The rate of temperature change in the atmosphere due to the raising or lowering of an air mass.
  73. atmospheric
    relating to or located in the atmosphere
    Atmosphere=One atmosphere is 14.7 pounds per square inch (105 Newtons per square meter); the average atmospheric pressure at sea level on Earth.
  74. atmospheric pressure
    the pressure exerted by the atmosphere
    Atmosphere=One atmosphere is 14.7 pounds per square inch (105 Newtons per square meter); the average atmospheric pressure at sea level on Earth.
  75. atoll
    an island consisting of a circular coral reef surrounding a lagoon
    Atoll=A circular reef that surrounds a lagoon and is bounded on the outside by deep water of the open sea.
  76. atom
    (physics and chemistry) the smallest component of an element having the chemical properties of the element
    Chemical bond=The linkage between atoms in molecules and between molecules and ions in crystals.
  77. atomic
    of or relating to or comprising atoms
    Conduction=The transport of heat by atomic or molecular motion.
  78. aurora
    an atmospheric phenomenon consisting of bands of light caused by charged solar particles following the earth's magnetic lines of force
    Aurora borealis=The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.
  79. aurora borealis
    the aurora of the northern hemisphere
    Aurora borealis=The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.
  80. automatic
    operating with minimal human intervention; independent of external control
    Convection=Fluid (gas or liquid) circulation driven by temperature and density differences; the transfer of heat by this automatic circulation (currents).
  81. avalanche
    a slide of large masses of snow and ice and mud down a mountain
    Avalanche=A large mass of material falling or sliding rapidly due to the force of gravity.
  82. average
    an intermediate scale value regarded as normal or usual
    Astronomical unit=(AU) The average distance from the Earth to the Sun; 1 AU is 149,597,870 kilometers (92,960,116 miles).
  83. axis
    a straight line through a body or figure that satisfies certain conditions
    Eccentricity=A value that defines the shape of an ellipse or planetary orbit; the ratio of the distance between the foci and the major axis.
  84. bacteria
    (microbiology) single-celled or noncellular spherical or spiral or rod-shaped organisms lacking chlorophyll that reproduce by fission; important as pathogens and for biochemical properties; taxonomy is difficult; often considered to be plants
    Anaerobic=Without oxygen; anaerobic bacteria are bacteria that live without oxygen.
  85. barometer
    an instrument that measures atmospheric pressure
    Altimeter=A barometer with a scale calibrated in units of elevation rather than pressure.
  86. barrier
    a structure or object that impedes free movement
    Barrier island=A long, narrow, low-lying island that extends parallel to the shoreline.
  87. barrier island
    a long narrow sandy island (wider than a reef) running parallel to the shore
    Barrier island=A long, narrow, low-lying island that extends parallel to the shoreline.
  88. barrier reef
    a long coral reef near and parallel to the shore
    Barrier reef=A reef separated from the coast by a deep, wide lagoon.
  89. basal
    serving as or forming a base
    Basal slip=Movement of the entire mass of a glacier along the bedrock.
  90. batholith
    large mass of intrusive igneous rock believed to have solidified deep within the earth
    Batholith=A large plutonic mass of intrusive rock with more than 100 square kilometers of surface exposed.
  91. bedrock
    solid unweathered rock lying beneath surface deposits of soil
    Basal slip=Movement of the entire mass of a glacier along the bedrock.
  92. benefit
    something that aids or promotes well-being
    Cost benefit analysis=A system of analysis that attempts to weigh the cost of an act or policy, such as pollution control, directly against the economic benefits.
  93. big bang
    (cosmology) the cosmic explosion that is hypothesized to have marked the origin of the universe
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  94. big bang theory
    (cosmology) the theory that the universe originated sometime between 10 billion and 20 billion years ago from the cataclysmic explosion of a small volume of matter at extremely high density and temperature
    The big bang theory postulates that 10 to 20 billion years ago, all matter exploded from an infinitely compressed state.
  95. biological
    pertaining to biology or to life and living things
    The fragments are clastic, but they are of biological origin.
  96. biomass
    the total mass of living matter in a given unit area
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  97. biome
    a major biotic community characterized by the dominant forms of plant life and the prevailing climate
    Biome=A community of plants living in a large geographic area characterized by a particular climate.
  98. bioremediation
    the branch of biotechnology that uses biological process to overcome environmental problems
    Bioremediation=The use of microorganisms to decompose an environmental contaminant.
  99. biosphere
    the regions of the surface and atmosphere of the Earth (or other planet) where living organisms exist
    Biosphere=The zone inhabited by life.
  100. bitumen
    any of various naturally occurring impure mixtures of hydrocarbons
    Bitumen=A general name for solid and semi-solid hydrocarbons that are fusible and soluble in carbon bisulfide.
  101. black hole
    a region of space resulting from the collapse of a star; extremely high gravitational field
    Black hole=An object whose gravity is so strong that the escape velocity exceeds the speed of light.
  102. black ice
    a thin coating of ice (as from freezing mist) on a road or sidewalk; nearly invisible but very hazardous
    Black ice=Thin, new ice on fresh or salt water that appears dark in color because of its transparency.
  103. blackbody
    a hypothetical object capable of absorbing all the electromagnetic radiation falling on it
    Blackbody temperature=The temperature of an object if it is reradiating all the thermal energy that has been added to it; if an object is not a blackbody radiator, it will not reradiate all the excess heat and the leftover will go toward increasing
  104. blizzard
    a storm with widespread snowfall accompanied by strong winds
    Blizzard conditions are common in a well-developed Alberta Clipper.
  105. blowout
    an easy victory
    Blowout=A small depression created by wind erosion.
  106. blue star
    subshrubs of southeastern United States forming slow-growing clumps and having blue flowers in short terminal cymes
    Blue stars=These are the hottest stars, with a surface temperature of more than 37,000°F.
    Body wave=A seismic wave that travel through the interior of the Earth.
  107. boil
    come to the boiling point and change from a liquid to vapor
    Boiling point=The temperature at which a liquid changes to a vaporous state.
  108. boiling point
    the temperature at which a liquid boils at sea level
    Boiling point=The temperature at which a liquid changes to a vaporous state.
  109. bolide
    an especially luminous meteor (sometimes exploding)
    The boiling point of pure water at standard pressure is 100°C or 212°F.
    Bolide=An exploding meteorite.
  110. boulder
    a large smooth mass of rock detached from its place of origin
    Cobbles=Rounded rock fragments in the 64 to 256 mm size range, larger than pebbles and smaller than boulders.
  111. Brahe
    Danish astronomer whose observations of the planets provided the basis for Kepler's laws of planetary motion (1546-1601)
    Johannes Kepler first discovered that the orbits of the planets are ellipses, not circles; he based his discovery on the careful observations of Tycho Brahe.
  112. breccia
    a rudaceous rock consisting of sharp fragments embedded in clay or sand
    Breccia=A course-grained rock, composed of angular, broken rock fragments held together by a mineral cement or a fine-grained matrix.
  113. brittle
    having little elasticity; hence easily cracked or fractured or snapped
    Brittle fracture=Rupture that occurs when a rock breaks sharply.
  114. broad
    having great (or a certain) extent from one side to the other
    Bajada=A broad depositional surface extending outward from a mountain front formed by the merging of alluvial fans.
  115. butte
    a hill that rises abruptly from the surrounding region; has a flat top and sloping sides
    A butte is smaller and more tower-like than a mesa.
  116. calcium
    a white metallic element that burns with a brilliant light; the fifth most abundant element in the earth's crust; an important component of most plants and animals
    Basalt=A dark-colored, very fine grained, mafic, volcanic rock composed of about half calcium-rich plagioclase feldspar and half pyroxene.
  117. calcium carbonate
    a salt found in nature as chalk or calcite or aragonite or limestone
    Caliche=A hard soil layer formed when calcium carbonate precipitates and cements the soil.
  118. caldera
    a large crater caused by the violent explosion of a volcano that collapses into a depression
    Caldera=A large circular depression caused by an explosive volcanic eruption.
  119. calorie
    unit of heat defined as the quantity of heat required to raise the temperature of 1 gram of water by 1 degree centigrade at atmospheric pressure
    Results in liberation of 80 calories per cubic centimeter.
  120. calving
    giving birth to a calf
    Calving=A process in which large chunks of ice break off from tidewater glaciers to form icebergs.
  121. capacity
    capability to perform or produce
    Capacity=The maximum quantity of sediment that a stream can carry.
  122. capillary
    any of the minute blood vessels connecting arterioles with venules
    Capillary action=The action by which water is pulled upward through small pores by electrical attraction to the pore walls.
  123. capillary action
    a phenomenon associated with surface tension and resulting in the elevation or depression of liquids in capillaries
    Capillary action=The action by which water is pulled upward through small pores by electrical attraction to the pore walls.
  124. capsule
    a small container
    Anemometer=an instrument that measures wind speed
    Aneriod Barometer=A barometer whose pressure sensor consists of an aneroid capsule, a thin, hollow disk partially evacuated and sealed.
  125. carbon
    an abundant nonmetallic tetravalent element occurring in three allotropic forms: amorphous carbon and graphite and diamond; occurs in all organic compounds
    Argon (A) at 0.93%; and Carbon Dioxide (CO2) 0.033%.
  126. carbon atom
    an atom of carbon
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  127. carbon dioxide
    a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesis
    Argon (A) at 0.93%; and Carbon Dioxide (CO2) 0.033%.
  128. carbonate
    treat with carbon dioxide
    Caliche=A hard soil layer formed when calcium carbonate precipitates and cements the soil.
  129. cascade
    a small waterfall or series of small waterfalls
    The major volcanic cones of the Cascade Mountains (in Washington, Oregon, and California) are believed to be dormant rather than extinct.
  130. cataclysmic
    severely destructive
    Catastrophism=The model that Earth change occurs through a series of rare but cataclysmic events.
  131. catalyst
    (chemistry) a substance that initiates or accelerates a chemical reaction without itself being affected
    In many cases, water acts as a catalyst and/or lubricant.
  132. cation
    a positively charged ion
    Cation=A positively charged ion.
  133. cavern
    a large cave or a large chamber in a cave
    Cavern=An underground cavity or series of chambers created when groundwater dissolves large amounts of rock, usually limestone. (syn: cave)
    Celestial sphere=An imaginary sphere around the Earth that all the stars and planets are placed on.
  134. celestial
    relating to or inhabiting a divine heaven
    Asteroid number=Asteroids are assigned a serial number when they are discovered; it has no particular meaning except that asteroid N+1 was discovered after asteroid N.
    Asteroid=One of the many small celestial bodies in orbit around the Sun. Most asteroids orbit between Mars and Jupiter.
  135. celestial body
    natural objects visible in the sky
    Asteroid number=Asteroids are assigned a serial number when they are discovered; it has no particular meaning except that asteroid N+1 was discovered after asteroid N.
    Asteroid=One of the many small celestial bodies in orbit around the Sun. Most asteroids orbit between Mars and Jupiter.
  136. celestial sphere
    the apparent surface of the imaginary sphere on which celestial bodies appear to be projected
    Cavern=An underground cavity or series of chambers created when groundwater dissolves large amounts of rock, usually limestone. (syn: cave)
    Celestial sphere=An imaginary sphere around the Earth that all the stars and planets are placed on.
  137. Celsius
    Swedish astronomer who devised the centigrade thermometer (1701-1744)
    Celsius and -459.67o
  138. Cenozoic
    of or relating to or denoting the Cenozoic era
    Cenozoic era=The latest of the four eras into which geologic time is subdivided; 65 million years ago to the present.
  139. center
    an area that is approximately central within some larger region
    Barchan dune=A crescent shaped dune, highest in the center, with the tips facing downwind.
  140. CFC
    a fluorocarbon with chlorine; formerly used as a refrigerant and as a propellant in aerosol cans
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=( CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  141. chain reaction
    a series of chemical reactions in which the product of one is a reactant in the next
    Branching chain reaction=A nuclear fission reaction in which the initial reaction releases two or three neutrons, each of which triggers the fission of additional nuclei.
  142. chamber
    a natural or artificial enclosed space
    Cavern=An underground cavity or series of chambers created when groundwater dissolves large amounts of rock, usually limestone. (syn: cave)
    Celestial sphere=An imaginary sphere around the Earth that all the stars and planets are placed on.
  143. channel
    a deep and relatively narrow body of water (as in a river or a harbor or a strait linking two larger bodies) that allows the best passage for vessels
    Antecedent stream=A stream that was established before local uplift started and cut its channel at the same rate the land wasrising.
  144. channels
    official routes of communication
    Braided stream=A stream that divides into a network of branching and reuniting shallow channels separated by mid-channel bars.
  145. character
    a characteristic property that defines the apparent individual nature of something
    Active continental margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: Andean margin)
    Active volcano=A volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
  146. chart
    a visual display of information
    This movement is amplified by a spring or gear mechanism to indicate changes in air pressure on a scale or recording chart.
  147. chemical
    of or made from or using substances produced by or used in reactions involving atomic or molecular changes
    Chemical bond=The linkage between atoms in molecules and between molecules and ions in crystals.
  148. chemical bond
    an electrical force linking atoms
    Chemical bond=The linkage between atoms in molecules and between molecules and ions in crystals.
  149. chemist
    a scientist who specializes in chemistry
    Atmospheric chemists divide the atmosphere into the heterosphere, where gases are well mixed, and the homosphere, where gases are found in differentiated layers.
  150. chert
    variety of silica containing microcrystalline quartz
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  151. chlorine
    a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  152. chlorofluorocarbon
    a fluorocarbon with chlorine; formerly used as a refrigerant and as a propellant in aerosol cans
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  153. chromosphere
    a gaseous layer of the sun's atmosphere (extending from the photosphere to the corona) that is visible during a total eclipse of the sun
    Chromosphere=A turbulent diffuse gaseous layer of the Sun that lies above the photosphere.
  154. cirque
    a steep-walled semicircular basin in a mountain; may contain a lake
    Cirque=A steep-walled horseshoe-shaped recess high on a mountain that is formed by glacial erosion.
  155. cirrus
    a wispy white cloud (usually of fine ice crystals) at a high altitude (4 to 8 miles)
    Cirrus=A principal cloud type present at high altitudes, generally above 7000 meters, and composed of ice crystals.
  156. clastic
    capable of being taken apart
    The fragments are clastic, but they are of biological origin.
  157. clastic rock
    (geology) a rock composed of broken pieces of older rocks
    Clastic rocks=sedimentary rocks formed from fragments of other rocks.
  158. cleavage
    the act of cleaving or splitting
    Cleavage=The way crystalline minerals split or break along an even plane (planar surfaces).
  159. climate
    the weather in some location averaged over some long period of time
    Biome=A community of plants living in a large geographic area characterized by a particular climate.
  160. clipper
    scissors for cutting hair or finger nails (often used in the plural)
    Alberta Clipper=A fast moving winter storm originating in the Alberta, Canada region.
  161. CO2
    a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesis
    Argon (A) at 0.93%; and Carbon Dioxide ( CO2) 0.033%.
  162. coast
    the shore of a sea or ocean
    Barrier reef=A reef separated from the coast by a deep, wide lagoon.
  163. cold front
    the front of an advancing mass of colder air
    Cold front=the leading edge of an advancing cold air mass that is under running and displacing the warmer air in its path.
  164. collapse
    break down, literally or metaphorically
    Degeneracy pressure=The strength of the atomic particles that holds a white dwarf star from further collapse.
  165. collide
    crash together with violent impact
    Cold front=A front that forms when moving cold air collides with stationary or slower moving warm air.
  166. column
    a line of units following one after another
    Column=A dripstone or speleothem formed when a stalactite and a stalagmite meet and fuse together.
  167. coma
    a state of deep and often prolonged unconsciousness; usually the result of disease or injury
    Coma=The dust and gas surrounding an active comet's nucleus.
  168. comet
    (astronomy) a relatively small extraterrestrial body consisting of a frozen mass that travels around the sun in a highly elliptical orbit
    Coma=The dust and gas surrounding an active comet's nucleus.
  169. competence
    the quality of being adequately or well qualified physically and intellectually
    Competence=A measure of the largest particles that a stream can transport.
  170. component
    an artifact that is one of the individual parts of which a composite entity is made up; especially a part that can be separated from or attached to a system
    Advection=In meteorology, the horizontal component of a convection current in air, i.e.
  171. compose
    form the substance of
    The principal gases that compose dry air are Nitrogen (N2) 78.09%;
  172. composite
    consisting of separate interconnected parts
    They occur with composite volcanic cones associated with convergent plate margins.
  173. compound
    a whole formed by a union of two or more elements or parts
    Carbonate=A compound containing carbon and oxygen; an example is calcium carbonate (limestone).
  174. compress
    squeeze or press together
    The big bang theory postulates that 10 to 20 billion years ago, all matter exploded from an infinitely compressed state.
  175. compression
    applying pressure
    Compression Waves=Earthquake waves that move like a slinky.
  176. concentration
    the spatial property of being crowded together
    Banded iron formation=Iron-rich layered sedimentary rocks precipitated from the seas mostly between 2.6 and 1.9 billion years ago, as a result of rising atmospheric oxygen concentrations.
  177. concentric
    having a common center
    Celestial spheres=A hypothetical series of concentric spheres centered at the center of the Earth.
  178. concerted
    involving the joint activity of two or more
    Current=A continuous flow of water in a concerted direction.
  179. condensation
    the process of changing from a gaseous to a liquid or solid state
    A cloud forms in the atmosphere as a result of condensation of water vapor.
  180. condense
    cause a gas or vapor to change into a liquid
    Advection fog=Fog that forms when warm moist air from the sea blows onto cooler land, where the air cools and water vapor condenses at ground level.
  181. conduction
    the transmission of heat or electricity or sound
    Conduction=the movement of heat to an object by its contact with a hotter object.
  182. cone
    a shape whose base is a circle and whose sides taper up to a point
    They occur with composite volcanic cones associated with convergent plate margins.
  183. confined
    being in captivity
    Artesian Well=A well in an aquifer where the groundwater is confined under pressure and the water level will rise above the top of the confined aquifer.
  184. confining
    restricting the scope or freedom of action
    Confining pressure=See "confining stress."
  185. conformable
    disposed or willing to comply
    Conformable=The condition in which sedimentary layers were deposited continuously without interruption.
  186. consecutive
    one after the other
    Contour interval=the difference in elevation between two consecutive contour lines
    Contour line=line on a topographic map that connects points on land that have the same elevation.
  187. consist
    have its essential character; be comprised or contained in; be embodied in
    Andesite=A fine-grained gray or green volcanic rock intermediate in composition between basalt and granite, consisting of about equal amounts of plagioclase feldspar and mafic minerals.
  188. conspicuous
    obvious to the eye or mind
    Butte=A conspicuous, isolated, flattop hill with steep slopes.
  189. constant
    uninterrupted in time and indefinitely long continuing
    Altitude=height (number of degrees) of an object above the horizon.In meteorology, the measure of a height of an airborne object in respect to a constant pressure surface or above mean sea level.
  190. constellation
    a configuration of stars as seen from the earth
    Constellation=a group of stars that appears to form a pattern in the sky.
  191. constituent
    an artifact that is one of the individual parts of which a composite entity is made up; especially a part that can be separated from or attached to a system
    One other important constituents of air is water vapor (H2O) which varies from 0% to about 4%.
  192. constitute
    form or compose
    Eccentricity=The shape of the ellipse that constitutes the Earth's orbit around the Sun.
    Echo sounder=An instrument that emits sound waves and then records them after they reflects off the sea floor.
  193. consumption
    the act of consuming something
    Consumption=Any process that uses water, and then returns it to the Earth far from its source.
  194. contact
    the act of touching physically
    The black color is caused by precipitation of very fine grained metal sulfide minerals as hydrothermal solutions cool by contact with sea water.
  195. contain
    contain or hold; have within
    Andean margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: active continental margin)
    Andesite=Intermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
  196. continent
    one of the large landmasses of the earth
    Accreted terrain=A land mass that originated as an island arc or a microcontinent that was later added onto a continent.
  197. continental drift
    the gradual movement and formation of continents (as described by plate tectonics)
    Continental Drift=The theory that horizontal movement of the earth's surface causes slow, relative movements of the continents toward or away from one another.
  198. continental shelf
    the relatively shallow (up to 200 meters) seabed surrounding a continent
    Carbonate platform=An extensive accumulation of limestone such as the Florida Keys and the Bahamas, formed on a continental shelf in warm regions where sediment does not muddy the water and reef-building organisms thrive.
  199. continental slope
    the steep descent of the seabed from the continental shelf to the abyssal zone
    Continental glacier=A glacier that forms a continuous cover of ice over areas of 50,000 square kilometers or more and spreads outward in all directions under the influence of its own weight. (syn: ice sheet)
    Continental margin=The region between the shoreline of a continent and the deep ocean basins including the continental shelf, continental slope, and continental rise.
  200. continuous
    continuing in time or space without interruption
    Continental glacier=A glacier that forms a continuous cover of ice over areas of 50,000 square kilometers or more and spreads outward in all directions under the influence of its own weight. (syn: ice sheet)
    Continental margin=The region between the shoreline of a continent and the deep ocean basins including the continental shelf, continental slope, and continental rise.
  201. contour
    a line drawn on a map connecting points of equal height
    Contour interval=the difference in elevation between two consecutive contour lines
    Contour line=line on a topographic map that connects points on land that have the same elevation.
  202. contour line
    a line drawn on a map connecting points of equal height
    Contour interval=the difference in elevation between two consecutive contour lines
    Contour line=line on a topographic map that connects points on land that have the same elevation.
  203. control rod
    a steel or aluminum rod that can be moved up or down to control the rate of the nuclear reaction
    Control rod=A column of neutron-absorbing alloys that are spaced among fuel rods to fine-tune nuclear fission in a reactor.
  204. convection
    the transfer of heat through a fluid (liquid or gas) caused by molecular motion
    Advection=In meteorology, the horizontal component of a convection current in air, i.e.
  205. convergence
    the act of converging (coming closer)
    Convergence=The flow of the wind resulting in a horizontal inflow of air into a region.
  206. convergent
    tending to come together from different directions
    They occur with composite volcanic cones associated with convergent plate margins.
  207. converted
    spiritually reborn or converted
    Desertification=A process by which semiarid land is converted to desert, often by improper farming or by climate change.
  208. convex
    curving or bulging outward
    Anticline=A fold in rock that resembles an arch; the fold is convex upward and the oldest rocks are in the middle Anticyclone: An area of high pressure, also called a High, around which the winds circulate in a clockwise direction in the Northern Hemisphere (and counterclockwise in the Southern Hemisphere).
  209. core
    the center of an object
    Core, inner=spherical center of the Earth, about 1200 km in diameter and made of solid iron and nickel.
  210. Coriolis effect
    (physics) an effect whereby a body moving in a rotating frame of reference experiences the Coriolis force acting perpendicular to the direction of motion and to the axis of rotation; on Earth the Coriolis effect deflects moving bodies to the right in the northern hemisphere and to the left in the southern hemisphere
    In the northern hemisphere, the Coriolis effect deflects the diverging winds to the right, forming a pinwheel pattern with the air spiraling clockwise.
  211. corona
    one or more circles of light seen around a luminous object
    Corona=The very hot outermost layer of a star's atmosphere.
  212. correlation
    a reciprocal relation between two or more things
    Corona=The luminous irregular envelope of highly ionized gas outside the chromosphere of the Sun.
    Correlation=the process of matching rock layers from different locations.
  213. cosmic
    of or from or pertaining to or characteristic of the cosmos or universe
    Cosmic ray=Electromagnetic rays of extremely high frequency and energy; cosmic rays usually interact with the atoms of the atmosphere before reaching the surface of the Earth.
  214. cosmic ray
    highly penetrating ionizing radiation of extraterrestrial origin; consisting chiefly of protons and alpha particles; collision with atmospheric particles results in rays and particles of many kinds
    Cosmic ray=Electromagnetic rays of extremely high frequency and energy; cosmic rays usually interact with the atoms of the atmosphere before reaching the surface of the Earth.
  215. Crater
    a faint constellation in the southern hemisphere near Hydra and Corvus
    Crater=A depression formed by the impact of a meteorite. 2) A depression around the orifice of a volcano.
  216. crater
    a bowl-shaped geological formation at the top of a volcano
    Ash Flow=A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure.
  217. craton
    the part of a continent that is stable and forms the central mass of the continent; typically Precambrian
    Craton=A segment of continental crust, usually in the interior of a continent, that has been tectonically stable for a long time commonly a billion years or longer.
  218. creep
    move slowly; in the case of people or animals with the body near the ground
    Creep=The slow movement of unconsolidated material downslope under the influence of gravity.
  219. Cretaceous
    of or relating to or denoting the third period of the Mesozoic era
    Cretaceous period=A geological term denoting the interval of Earth history beginning around 144 million years ago and ending 66 million years ago.
  220. crevasse
    a deep fissure
    The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. see Key bed
    Crevasse=A fracture or crack in the upper 40 to 50 meters of a glacier.
  221. crystalline
    consisting of or containing or of the nature of crystals
    Cleavage=The way crystalline minerals split or break along an even plane (planar surfaces).
  222. cumulonimbus
    a dark cloud of great vertical extent charged with electricity; associated with thunderstorms
    The dense, cold air distorts into a blunt wedge and pushes under the warmer air, creating a narrow band of violent weather commonly accompanied by cumulus and cumulonimbus clouds.
  223. cumulus
    a globular cloud
    The dense, cold air distorts into a blunt wedge and pushes under the warmer air, creating a narrow band of violent weather commonly accompanied by cumulus and cumulonimbus clouds.
  224. current
    occurring in or belonging to the present time
    Advection=In meteorology, the horizontal component of a convection current in air, i.e.
  225. cycle
    a periodically repeated sequence of events
    Climate refers to yearly cycles of temperature, wind, rainfall, etc., and not to daily variations (see "weather").
  226. cyclical
    recurring in cycles
    Effluent stream=A stream that receives water from groundwater because its channel lies below the water table. (syn: gaining stream)
    El Nino=(Niño, Nin~o) The cyclical warming of East Pacific Ocean sea water temperatures off the western coast of South America that can result in significant changes in weather patterns in the United States and elsewhere.
  227. cyclone
    (meteorology) rapid inward circulation of air masses about a low pressure center; circling counterclockwise in the northern hemisphere and clockwise in the southern
    Anticyclonic=The wind circulation pattern in Highs, or anticyclones, that has a sense of rotation opposite to that of cyclones and the Earth's rotation.
  228. cyclonic
    of or relating to or characteristic of the atmosphere around a low pressure center
    Cyclonic=Air flow around the center of a surface Low. In the Northern Hemisphere, this flow is counterclockwise as seen from above.
  229. data
    a collection of facts from which conclusions may be drawn
    The data is then used to record the topography of the sea floor.
  230. debris
    the remains of something that has been destroyed or broken up
    A mixture of these materials is commonly called a debris flow.
  231. decay
    the organic phenomenon of rotting
    Absolute Date=An estimate of the true age of a mineral or rock based on the rate of decay of radioactive minerals.
  232. decompose
    separate (substances) into constituent elements or parts
    Bioremediation=The use of microorganisms to decompose an environmental contaminant.
  233. decomposition
    the organic phenomenon of rotting
    Chemical weathering=breakdown or decomposition of a rock that takes place when minerals are changed into different substances.
  234. decrease
    a change downward
    Generally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises, and the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere).
  235. define
    show the form or outline of
    Eccentricity=A value that defines the shape of an ellipse or planetary orbit; the ratio of the distance between the foci and the major axis.
  236. defined
    showing clearly the outline or profile or boundary
    The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. see Key bed
    Crevasse=A fracture or crack in the upper 40 to 50 meters of a glacier.
  237. definition
    a concise explanation of the meaning of a word or phrase or symbol
    Blizzard=Although blizzard is often used to describe any major snow storm with strong winds, the technical definition for a blizzard requires at least 3 hours in duration; low temperatures (usually less than minus 7C or 20F), strong winds (greater than 55 km/h or 35 mph), blowing snow which reduces visibility to less that 1 kilometer (0.6 miles).
  238. deflation
    the act of letting the air out of something
    Deflation=Erosion by wind.
  239. deflect
    turn from a straight course, fixed direction, or line of interest
    In the northern hemisphere, the Coriolis effect deflects the diverging winds to the right, forming a pinwheel pattern with the air spiraling clockwise.
  240. degree
    a specific identifiable position in a continuum or series or especially in a process
    Altitude=height (number of degrees) of an object above the horizon.In meteorology, the measure of a height of an airborne object in respect to a constant pressure surface or above mean sea level.
  241. delta
    the 4th letter of the Greek alphabet
    Delta=A fan-shaped deposit of sediment formed at the mouth of a stream or river.
  242. demise
    the time when something ends
    The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. see Key bed
    Crevasse=A fracture or crack in the upper 40 to 50 meters of a glacier.
  243. demonstration
    a show or display; the act of presenting something to sight or view
    Correlation= Demonstration of the equivalence of rocks or geologic features age from different locations.
  244. dense
    hard to pass through because of dense growth
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  245. density
    the amount per unit size
    Absolute Humidity=The ratio of the mass of water vapor present in the air to the volume occupied by the gas; the density of water vapor in the air, usually expressed as grams of water vapor per cubic meter of air.
  246. deposit
    the act of putting something somewhere
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  247. deposition
    the act of putting something somewhere
    Deposition=The laying-down of rock-forming materials by any natural agent.
  248. depression
    a sunken or depressed geological formation
    Blowout=A small depression created by wind erosion.
  249. descend
    move downward and lower, but not necessarily all the way
    Anticyclone=A system of rotating winds that develop where descending air spreads out over the Earth's surface.
  250. describe
    give a description of
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  251. desert
    leave someone who needs or counts on you; leave in the lurch
    Example: crater
    Desert pavement=A continuous cover of stones created as wind erodes fine sediment, leaving larger rocks behind.
  252. desertification
    the gradual transformation of habitable land into desert; is usually caused by climate change or by destructive use of the land
    Desertification=A process by which semiarid land is converted to desert, often by improper farming or by climate change.
  253. develop
    grow, progress, unfold, or evolve through a process of evolution, natural growth, differentiation, or a conducive environment
    Aa flows commonly developed from pahoehoe flows as they cool and lose gas.
  254. Devonian
    from 405 million to 345 million years ago; preponderance of fishes and appearance of amphibians and ammonites
    Devonian=A period of time in the Paleozoic Era that covered the time span between 408 and 360 million years.
  255. dew
    water that has condensed on a cool surface overnight from water vapor in the air
    Dew Point=(or Dew Point Temperature) The temperature to which air must be cooled for saturation to occur.
  256. dew point
    the temperature at which the water vapor in the air becomes saturated and condensation begins
    Dew Point=(or Dew Point Temperature) The temperature to which air must be cooled for saturation to occur.
  257. diameter
    the length of a straight line passing through the center of a circle and connecting two points on the circumference
    Ash=(volcanic) Fine pyroclastic material less than 2 mm in diameter.
  258. differential
    a quality that differentiates between similar things
    Differential weathering=The process by which certain rocks weathers more rapidly than adjacent rocks usually resulting in an uneven surface.
  259. differentiated
    made different (especially in the course of development) or shown to be different
    Atmospheric chemists divide the atmosphere into the heterosphere, where gases are well mixed, and the homosphere, where gases are found in differentiated layers.
  260. diffuse
    spread out; not concentrated in one place
    Chromosphere=A turbulent diffuse gaseous layer of the Sun that lies above the photosphere.
  261. dinosaur
    any of numerous extinct terrestrial reptiles of the Mesozoic era
    Cretaceous-Tertiary boundary=A major stratigraphic boundary on Earth marking the end of the Mesozoic Era, best known as the age of the dinosaurs.
  262. dioxide
    an oxide containing two atoms of oxygen in the molecule
    Argon (A) at 0.93%; and Carbon Dioxide (CO2) 0.033%.
  263. direction
    a line leading to a place or point
    Anticline=A fold in rock that resembles an arch; the fold is convex upward and the oldest rocks are in the middle Anticyclone: An area of high pressure, also called a High, around which the winds circulate in a clockwise direction in the Northern Hemisphere (and counterclockwise in the Southern Hemisphere).
  264. discordant
    not in agreement or harmony
    Discordant=Pertaining to a dike or other feature that cuts across sedimentary layers or other kinds of layering in country rock.
  265. disk
    something with a round shape resembling a flat circular plate
    Anemometer=an instrument that measures wind speed
    Aneriod Barometer=A barometer whose pressure sensor consists of an aneroid capsule, a thin, hollow disk partially evacuated and sealed.
  266. displace
    cause to move, usually with force or pressure
    This occurs when warm equatorial waters move in and displace the colder waters of the Peru Current, cutting off the upwelling process.
  267. dissolve
    pass into a solution
    Cavern=An underground cavity or series of chambers created when groundwater dissolves large amounts of rock, usually limestone. (syn: cave)
    Celestial sphere=An imaginary sphere around the Earth that all the stars and planets are placed on.
  268. distort
    twist and press out of shape
    The dense, cold air distorts into a blunt wedge and pushes under the warmer air, creating a narrow band of violent weather commonly accompanied by cumulus and cumulonimbus clouds.
  269. distributary
    a branch of a river that flows away from the main stream and does not rejoin it
    Distributary=A channel that flows outward from the main stream channel, such as is commonly found in deltas.
  270. distribution
    the act of distributing or spreading or apportioning
    Epidemiology=The study of the distribution of sickness in a population.
  271. divergence
    the act of moving away in different direction from a common point
    The opposite of convergence is divergence.
  272. divergent
    tending to move apart in different directions
    Continental rifting=The process by which a continent is pulled apart at a divergent plate boundary.
  273. diversion
    a turning aside (of your course or attention or concern)
    Diversion=All processes that transfer ground or surface water from its natural place and path in the hydrologic cycle to a new place and path to serve human needs.
  274. divide
    a serious disagreement between two groups of people (typically producing tension or hostility)
    Atmospheric chemists divide the atmosphere into the heterosphere, where gases are well mixed, and the homosphere, where gases are found in differentiated layers.
  275. division
    the act of dividing or partitioning; separation by the creation of a boundary that divides or keeps apart
    Archean Eon=A division of geologic time 3.8 to 2.5 billion years ago.
  276. doldrums
    a belt of calms and light winds between the northern and southern trade winds of the Atlantic and Pacific
    Doldrums=the rainy equatorial belt of low pressure and slowly rising air.
  277. dome
    a concave shape whose distinguishing characteristic is that the concavity faces downward
    Compound Volcano=A volcano that consists of a complex of two or more vents, or a volcano that has an associated volcanic dome, either in its crater or on its flanks.
  278. Doppler
    Austrian physicist famous for his discovery of the Doppler effect (1803-1853)
    Doppler effect=The apparent change in wavelength of sound or light caused by the motion of the source, observer or both.
  279. Doppler effect
    change in the apparent frequency of a wave as observer and source move toward or away from each other
    Doppler effect=The apparent change in wavelength of sound or light caused by the motion of the source, observer or both.
  280. dormant
    inactive but capable of becoming active
    Dormant volcano=This term is used to describe a volcano which is presently inactive but which may erupt again.
  281. downstream
    in the direction of a stream's current
    Discharge=The volume of water flowing downstream per unit time.
  282. drain
    emptying something accomplished by allowing liquid to run out of it
    Drainage Basin=The area of land drained by a river system.
  283. drainage basin
    the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet
    Divide=The higher land separating two adjacent drainage basins.
  284. drift
    be in motion due to some air or water current
    Often these snow storms have high winds reaching 100 km/h which reduce visibility through blowing and drifting snow.
  285. dripstone
    the form of calcium carbonate found in stalactites and stalagmites
    Column=A dripstone or speleothem formed when a stalactite and a stalagmite meet and fuse together.
  286. drizzle
    very light rain; stronger than mist but less than a shower
    They are smaller in size than either drizzle or rain drops.
  287. drought
    a shortage of rainfall
    Drought=Abnormal dry weather for a specific area that is sufficiently prolonged for the lack of water to cause serious hydrological imbalance.
  288. drumlin
    a mound of glacial drift
    Drumlin=a long, canoe-shaped hill made of till and shaped by an advancing glacier.
  289. dune
    a ridge of sand created by the wind; found in deserts or near lakes and oceans
    Barchan dune=A crescent shaped dune, highest in the center, with the tips facing downwind.
  290. duration
    the period of time during which something continues
    Blizzard=Although blizzard is often used to describe any major snow storm with strong winds, the technical definition for a blizzard requires at least 3 hours in duration; low temperatures (usually less than minus 7C or 20F), strong winds (greater than 55 km/h or 35 mph), blowing snow which reduces visibility to less that 1 kilometer (0.6 miles).
  291. dust bowl
    a region subject to dust storms; especially the central region of United States subject to dust storms in the 1930s
    Dust Bowl=The term given to the area of the Great Plains including Texas, Oklahoma, Kansas, Colorado, and New Mexico that was most greatly affected during the Great Drought of the 1930's.
  292. earth
    the 3rd planet from the sun; the planet we live on
    Air pressure=(barometric pressure) weight of the atmosphere per unit area
    Air=The mixture of gases that make up the earth's atmosphere.
  293. earthquake
    shaking and vibration at the surface of the earth resulting from underground movement along a fault plane of from volcanic activity
    Aseismic ridge=A submarine mountain chain with little or no earthquake activity.
  294. earthy
    of or consisting of or resembling earth
    Chalk=A very fine grained, soft, earthy, white to gray bioclastic limestone made of the shells and skeletons of marine microorganisms.
  295. eccentric
    conspicuously or grossly unconventional or unusual
    Eccentric=Noncircular; elliptical (applied to an orbit).
  296. eccentricity
    strange and unconventional behavior
    Eccentricity=A value that defines the shape of an ellipse or planetary orbit; the ratio of the distance between the foci and the major axis.
  297. echo sounder
    a measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return
    Eccentricity=The shape of the ellipse that constitutes the Earth's orbit around the Sun.
    Echo sounder=An instrument that emits sound waves and then records them after they reflects off the sea floor.
  298. eclipse
    one celestial body obscures another
    Our Sun's corona can only be seen during a total solar eclipse.
  299. ecliptic
    the great circle representing the apparent annual path of the sun; the plane of the Earth's orbit around the sun; makes an angle of about 23 degrees with the equator
    Ecliptic=The plane of Earth's orbit about the Sun. The sun's apparent path across the sky that tracks a circle through the celestial sphere.
  300. economical
    using the minimum of time or resources necessary for effectiveness
    Disseminated ore deposit=A large low-grade ore deposit in which generally fine-grained metal-bearing minerals are widely scattered throughout a rock body in sufficient concentration to make the deposit economical to mine.
  301. economically
    in an economical manner
    Aquifer=A porous and permeable body of rock that can yield economically significant quantities of ground water.
  302. edge
    a line determining the limits of an area
    Cold front=the leading edge of an advancing cold air mass that is under running and displacing the warmer air in its path.
  303. effect
    a phenomenon that follows and is caused by some previous phenomenon
    In the northern hemisphere, the Coriolis effect deflects the diverging winds to the right, forming a pinwheel pattern with the air spiraling clockwise.
  304. Einstein
    physicist born in Germany who formulated the special theory of relativity and the general theory of relativity; Einstein also proposed that light consists of discrete quantized bundles of energy (later called photons) (1879-1955)
    E=mc2 Einstein's famous theory of relativity formula known as the energy-mass relation.
  305. eject
    put out or expel from a place
    Ash Flow=A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure.
  306. El Nino
    (oceanography) a warm ocean current that flows along the equator from the date line and south off the coast of Ecuador at Christmas time
    Effluent stream=A stream that receives water from groundwater because its channel lies below the water table. (syn: gaining stream)
    El Nino=(Niño, Nin~o) The cyclical warming of East Pacific Ocean sea water temperatures off the western coast of South America that can result in significant changes in weather patterns in the United States and elsewhere.
  307. elastic
    capable of resuming original shape after stretching or compression; springy
    Earthquake=A sudden motion or trembling of the Earth caused by the abrupt release of slowly accumulated elastic energy in rocks.
  308. electrical
    relating to or concerned with electricity
    Capillary action=The action by which water is pulled upward through small pores by electrical attraction to the pore walls.
  309. electromagnetic
    pertaining to or exhibiting magnetism produced by electric charge in motion
    Cosmic ray= Electromagnetic rays of extremely high frequency and energy; cosmic rays usually interact with the atoms of the atmosphere before reaching the surface of the Earth.
  310. electromagnetic radiation
    radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge
    Electromagnetic radiation=The transfer of energy by an oscillating electric and magnetic field; it travels as a wave and also behaves as a stream of particles.
  311. electromagnetic spectrum
    the entire frequency range of electromagnetic waves
    Electromagnetic spectrum=total range of electromagnetic waves, from radio waves to gamma waves.
  312. electromagnetic wave
    radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge
    Electromagnetic spectrum=total range of electromagnetic waves, from radio waves to gamma waves.
  313. electron
    an elementary particle with negative charge
    Electron=A fundamental particle which forms a diffuse cloud of negative charge around an atom.
  314. electronic
    of or relating to electronics; concerned with or using devices that operate on principles governing the behavior of electrons
    There are three common types of barometers used widely today: mercury barometer; aneroid barometer; electronic barometer.
  315. element
    any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
    Compound=A pure substance composed of two or more elements whose composition is constant.
  316. elements
    violent or severe weather (viewed as caused by the action of the four elements)
    Compound=A pure substance composed of two or more elements whose composition is constant.
  317. ellipsis
    omission or suppression of parts of words or sentences
    Johannes Kepler first discovered that the orbits of the planets are ellipses, not circles; he based his discovery on the careful observations of Tycho Brahe.
  318. elliptical
    rounded like an egg
    Dome=A circular or elliptical anticlinal structure.
  319. elongate
    make long or longer by pulling and stretching
    Bar=An elongate mound of sediment, usually composed of sand or gravel, in a stream channel or along a coastline.
  320. emergent
    coming into existence
    Emergent coastline=A coastline that was recently under water but has been exposed either because the land has risen or sea level has fallen.
  321. emission
    the act of emitting; causing to flow forth
    Emission nebula=A glowing cloud of interstellar gas.
  322. emission spectrum
    spectrum of electromagnetic radiation emitted by a self-luminous source
    Emission spectrum=See "spectrum."
  323. emit
    give off, send forth, or discharge; as of light, heat, or radiation, vapor, etc.
    Some cosmic rays come from outside the solar system while others are emitted from the Sun and pass through holes in the corona.
  324. energy
    forceful exertion
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  325. entire
    constituting the full quantity or extent; complete
    Basal slip=Movement of the entire mass of a glacier along the bedrock.
  326. entry
    the act of entering
    See glossary entries for more on these types.
  327. environment
    the totality of surrounding conditions
    Chemical weathering=The chemical decomposition of rocks and minerals by exposure to air, water, and other chemicals in the environment.
  328. environmental
    of or relating to the external conditions or surroundings
    Bioremediation=The use of microorganisms to decompose an environmental contaminant.
  329. eon
    the longest division of geological time
    Archean Eon=A division of geologic time 3.8 to 2.5 billion years ago.
  330. epicenter
    the point on the Earth's surface directly above the focus of an earthquake
    Epicenter=the point on Earth's surface directly above the focus of an earthquake.
  331. epidemiology
    the branch of medical science dealing with the transmission and control of disease
    Epidemiology=The study of the distribution of sickness in a population.
  332. epoch
    a period marked by distinctive character or reckoned from a fixed point or event
    Epoch=a subdivision of a geological period on the geologic timetable.
  333. equal
    having the same quantity, value, or measure as another
    Andesite=A fine-grained gray or green volcanic rock intermediate in composition between basalt and granite, consisting of about equal amounts of plagioclase feldspar and mafic minerals.
  334. equator
    an imaginary line around the Earth forming the great circle that is equidistant from the north and south poles
    Coriolis Effect=the effect of Earth's rotation that causes the deflection of moving objects towards or away from the equator.
  335. equilibrium
    a stable situation in which forces cancel one another
    The temperature at which the equilibrium vapor pressure between a liquid and its vapor is equal to the external pressure on the liquid.
  336. equinox
    either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length
    Autumnal Equinox=see Equinox
    Autumnal=Pertaining to the Autumn season.
  337. equivalence
    essential equality and interchangeability
    Correlation=Demonstration of the equivalence of rocks or geologic features age from different locations.
  338. era
    a period marked by distinctive character or reckoned from a fixed point or event
    Cenozoic era=The latest of the four eras into which geologic time is subdivided; 65 million years ago to the present.
  339. erode
    remove soil or rock
    Base level=The deepest level to which a stream can erode its bed.
  340. eroded
    worn away as by water or ice or wind
    Angular unconformity=An unconformity in which younger sediment or sedimentary rocks rest on the eroded surface of tilted orfolded older rocks.
  341. erosion
    (geology) the mechanical process of wearing or grinding something down (as by particles washing over it)
    The oldest known rocks formed at the beginning of or just prior to the start of the Archean Eon.
    Arête=A sharp narrow ridge between adjacent valleys formed by glacial erosion.
  342. erratic
    liable to sudden unpredictable change
    Erratic=(glacial) Large rocks or other debris deposited by a glacier, usually in an area far removed from its source.
  343. erupt
    start abruptly
    Active continental margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: Andean margin)
    Active volcano=A volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
  344. eruption
    the sudden occurrence of a violent discharge of steam and volcanic material
    Ash flow=A mixture of volcanic ash, larger pyroclastic particles, and gas that flows rapidly along the Earth's surface as a result of an explosive volcanic eruption. (syn: nuee ardente)
    Ash=flow tuff-A pyroclastic rock formed when an ash flow solidifies.
  345. eruptive
    producing or characterized by eruptions
    Eruptive Vent=The opening through which volcanic material is emitted.
  346. escape velocity
    the minimum velocity needed to escape a gravitational field
    Black hole=An object whose gravity is so strong that the escape velocity exceeds the speed of light.
  347. esker
    (geology) a long winding ridge of post glacial gravel and other sediment; deposited by meltwater from glaciers or ice sheets
    Esker=a long, winding ridge formed when sand and gravel fill meltwater tunnels beneath a glacier.
  348. estuary
    the wide part of a river where it nears the sea; fresh and salt water mix
    Estuary=A bay that formed when a broad river valley was submerged by rising sea level or a sinking coast.
  349. eutrophic
    (ecology) of a lake or other body of water rich in nutrients and subject to eutrophication
    Eutrophic lake=A lake characterized by abundant dissolved nitrates, phosphates, and other plant nutrients and by a seasonal deficiency of oxygen in bottom water.
  350. evacuate
    move out of an unsafe location into safety
    Evacuate=Temporarily move people away from possible danger.
  351. evaporate
    change into a vapor
    The water evaporates, but the vapor cools and condenses to fog.
  352. evaporative
    relating to or causing or being caused by evaporation
    Downbursts occur in regions of a severe thunderstorm where the air is accelerated downward by exceptionally strong evaporative cooling occurs (a dry downburst) or by very heavy rain which drags dry air down with it (a wet downburst).
  353. event
    something that happens at a given place and time
    Absolute dating=A technique that geologists use to assign specific dates to rock formations and geologic events.
  354. exceed
    be or do something to a greater degree
    Accumulation area=The upper part of a glacier where accumulation of snow during the winter exceeds melting during the summer, causing a net gain of glacial ice.
  355. excess
    the state of being more than full
    Blackbody temperature=The temperature of an object if it is reradiating all the thermal energy that has been added to it; if an object is not a blackbody radiator, it will not reradiate all the excess heat and the leftover will go toward increasing its temperature.
  356. exert
    put to use
    Barometric pressure=The pressure exerted by the atmosphere at a given point.
  357. exosphere
    the outermost atmospheric layer
    The most common layer designations are: the troposphere, the stratosphere, the mesosphere and the exosphere.
  358. expand
    extend in one or more directions
    The difference between the exterior air pressure and the interior pressure causes the disk to expand or contract slightly.
  359. exposure
    the state of being vulnerable or exposed
    Aspect=The orientation of a slope with respect to the Sun; the geographic orientation or exposure of a slope.
  360. extend
    stretch out over a distance, space, time, or scope; run or extend between two points or beyond a certain point
    Antarctic Ozone Hole=An extended area of extreme depletion of the ozone layer which forms over the southern polar region eachaustral spring (September through November).
  361. extinct
    no longer in existence; lost or especially having died out leaving no living representatives
    The major volcanic cones of the Cascade Mountains (in Washington, Oregon, and California) are believed to be dormant rather than extinct.
  362. extinction
    no longer in existence
    The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. see Key bed
    Crevasse=A fracture or crack in the upper 40 to 50 meters of a glacier.
  363. Fahrenheit
    of or relating to a temperature scale proposed by the inventor of the mercury thermometer
    Fahrenheit.
  364. fan
    a device for creating a current of air by movement of a surface or surfaces
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  365. faucet
    a regulator for controlling the flow of a liquid from a reservoir
    When the rapidly descending air strikes the ground, it spreads outward in all directions in a circle, like a fast-running faucet hitting the sink bottom.
  366. feature
    a prominent attribute or aspect of something
    Correlation=Demonstration of the equivalence of rocks or geologic features age from different locations.
  367. fine-grained
    consisting of fine particles
    Andesite=A fine-grained gray or green volcanic rock intermediate in composition between basalt and granite, consisting of about equal amounts of plagioclase feldspar and mafic minerals.
  368. fine-tune
    make fine adjustments or divide into marked intervals for optimal measuring
    Control rod=A column of neutron-absorbing alloys that are spaced among fuel rods to fine-tune nuclear fission in a reactor.
  369. fission
    reproduction of some unicellular organisms by division of the cell into two more or less equal parts
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  370. fissure
    a long narrow depression in a surface
    Ash Flow=A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure.
  371. flammable
    easily ignited
    Coal=A flammable organic sedimentary rock formed from partially decomposed plant material and composed mainly of carbon.
  372. flint
    a hard kind of stone; a form of silica more opaque than chalcedony
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  373. flood
    the rising of a body of water and its overflowing onto normally dry land
    Artificial levee=A wall built along the banks of a stream to prevent rising flood water from spilling out of the stream channel onto the flood plain.
  374. flood plain
    a low plain adjacent to a river that is formed chiefly of river sediment and is subject to flooding
    Artificial levee=A wall built along the banks of a stream to prevent rising flood water from spilling out of the stream channel onto the flood plain.
  375. fluid
    continuous amorphous matter that tends to flow and to conform to the outline of its container: a liquid or a gas
    Contact metamorphism=Metamorphism caused by heating of country rock, and/or addition of fluids, from a nearby igneous intrusion.
  376. fluorine
    a nonmetallic univalent element belonging to the halogens; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  377. focus
    the concentration of attention or energy on something
    Eccentricity=A value that defines the shape of an ellipse or planetary orbit; the ratio of the distance between the foci and the major axis.
  378. formula
    a group of symbols that make a mathematical statement
    E=mc2 Einstein's famous theory of relativity formula known as the energy-mass relation.
  379. fossil
    the remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  380. fracture
    breaking of hard tissue such as bone
    Black smoker=A jet of black water spouting from a fracture in the sea floor, commonly near the mid-oceanic ridge.
  381. friction
    the resistance encountered when one body is moved in contact with another
    Abrasion=The mechanical wearing and grinding of rock surfaces by friction and impact.
  382. fuel
    a substance that can be consumed to produce energy
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  383. fundamental
    serving as an essential component
    Cross cutting relationships=A fundamental principle of geology, which states that rocks that cut through other rocks are younger than the rocks being cut.
  384. fundamental particle
    (physics) a particle that is less complex than an atom; regarded as constituents of all matter
    Electron=A fundamental particle which forms a diffuse cloud of negative charge around an atom.
  385. fuse
    any igniter that is used to initiate the burning of a propellant
    Column=A dripstone or speleothem formed when a stalactite and a stalagmite meet and fuse together.
  386. fusion
    the act of fusing (or melting) together
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  387. galaxy
    (astronomy) a collection of star systems; any of the billions of systems each having many stars and nebulae and dust
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  388. gamma
    the 3rd letter of the Greek alphabet
    Electromagnetic spectrum=total range of electromagnetic waves, from radio waves to gamma waves.
  389. gaseous
    existing as or having characteristics of a gas
    Chromosphere=A turbulent diffuse gaseous layer of the Sun that lies above the photosphere.
  390. gear
    a toothed wheel that engages another toothed mechanism in order to change the speed or direction of transmitted motion
    This movement is amplified by a spring or gear mechanism to indicate changes in air pressure on a scale or recording chart.
  391. geocentric
    having the earth as the center
    Epicycle=a small orbit along which a planet traveled in Ptolemy's geocentric model of the solar system.
  392. geologic
    of or relating to or based on geology
    Absolute dating=A technique that geologists use to assign specific dates to rock formations and geologic events.
  393. geologic time
    the time of the physical formation and development of the earth (especially prior to human history)
    Archean Eon=A division of geologic time 3.8 to 2.5 billion years ago.
  394. geological
    of or relating to or based on geology
    Cretaceous period=A geological term denoting the interval of Earth history beginning around 144 million years ago and ending 66 million years ago.
  395. geologist
    a specialist in geology
    Absolute dating=A technique that geologists use to assign specific dates to rock formations and geologic events.
  396. geology
    a science that deals with the history of the earth as recorded in rocks
    Cross cutting relationships=A fundamental principle of geology, which states that rocks that cut through other rocks are younger than the rocks being cut.
  397. geothermal
    of or relating to the heat in the interior of the earth
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  398. gigantic
    so exceedingly large or extensive as to suggest a giant or mammoth
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  399. glacial
    relating to or derived from a glacier
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  400. glacier
    a slowly moving mass of ice
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  401. global
    involving the entire earth; not limited or provincial in scope
    The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. see Key bed
    Crevasse=A fracture or crack in the upper 40 to 50 meters of a glacier.
  402. globe
    an object with a spherical shape
    On the date of the equinox (literally, meaning "equal nights") nights are of equal length all across the globe from pole to pole.
  403. glossary
    an alphabetical list of technical terms in some specialized field of knowledge; usually published as an appendix to a text on that field
    See glossary entries for more on these types.
  404. grade
    a position on a scale of intensity or amount or quality
    C horizon=The lowest soil layer composed of partly weathered bedrock grading downward into unweathered parent rock.
  405. grading
    evaluation of performance by assigning a grade or score
    C horizon=The lowest soil layer composed of partly weathered bedrock grading downward into unweathered parent rock.
  406. grain
    a cereal grass
    Andesite=A fine- grained gray or green volcanic rock intermediate in composition between basalt and granite, consisting of about equal amounts of plagioclase feldspar and mafic minerals.
  407. gravitational
    of or relating to or caused by gravitation
    Black hole=A small region of space that contains matter packed so densely that light cannot escape from its intense gravitational field.
  408. gravitational field
    a field of force surrounding a body of finite mass
    Black hole=A small region of space that contains matter packed so densely that light cannot escape from its intense gravitational field.
  409. gravity
    (physics) the force of attraction between all masses in the universe; especially the attraction of the earth's mass for bodies near its surface
    Atmosphere=The envelope of gases that surround a planet's surface held by the planet's gravity.
  410. ground level
    the height of the ground on which something stands
    Advection fog=Fog that forms when warm moist air from the sea blows onto cooler land, where the air cools and water vapor condenses at ground level.
  411. ground water
    underground water that is held in the soil and in pervious rocks
    Aquifer=A porous and permeable body of rock that can yield economically significant quantities of ground water.
  412. H2O
    binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 degrees centigrade and boils above 100 degrees centigrade; widely used as a solvent
    One other important constituents of air is water vapor ( H2O) which varies from 0% to about 4%.
  413. heat energy
    a form of energy that is transferred by a difference in temperature
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  414. heavenly body
    natural objects visible in the sky
    Disk=The visible surface of the Sun (or any heavenly body) projected against the sky.
  415. hemisphere
    half of a sphere
    Anticline=A fold in rock that resembles an arch; the fold is convex upward and the oldest rocks are in the middle Anticyclone: An area of high pressure, also called a High, around which the winds circulate in a clockwise direction in the Northern Hemisphere (and counterclockwise in the Southern Hemisphere).
  416. high frequency
    3 to 30 megahertz
    Cosmic ray=Electromagnetic rays of extremely high frequency and energy; cosmic rays usually interact with the atoms of the atmosphere before reaching the surface of the Earth.
  417. high-level
    at an elevated level in rank or importance
    Altostratus cloud=A high-level stratus cloud.
  418. horizon
    the line at which the sky and Earth appear to meet
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  419. humid
    containing or characterized by a great deal of water vapor
    A cloud-like streamer or trail often seen behind aircraft flying in clear, cold, humid air.
  420. humidity
    wetness in the atmosphere
    Absolute Humidity=The ratio of the mass of water vapor present in the air to the volume occupied by the gas; the density of water vapor in the air, usually expressed as grams of water vapor per cubic meter of air.
  421. hurricane
    a severe tropical cyclone usually with heavy rains and winds moving a 73-136 knots (12 on the Beaufort scale)
    Also a synonym for a tropical cyclone, or hurricane.
  422. hydrocarbon
    an organic compound containing only carbon and hydrogen
    Bitumen=A general name for solid and semi-solid hydrocarbons that are fusible and soluble in carbon bisulfide.
  423. hydroelectric
    of or relating to or used in the production of electricity by waterpower
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  424. hydrogen
    a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  425. hydroxide
    a compound of an oxide with water
    Bauxite=A gray, yellow, or reddish brown rock composed of a mixture of aluminum oxides and hydroxides.
  426. hypothesis
    a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  427. hypothetical
    a hypothetical possibility, circumstance, statement, proposal, situation, etc.
    Celestial spheres=A hypothetical series of concentric spheres centered at the center of the Earth.
  428. iceberg
    a large mass of ice floating at sea; usually broken off of a polar glacier
    Calving=A process in which large chunks of ice break off from tidewater glaciers to form icebergs.
  429. identical
    being the exact same one; not any other:
    The temperature recorded is considered identical to air temperature.
  430. igneous
    produced by the action of fire or intense heat
    Contact metamorphism=Metamorphism caused by heating of country rock, and/or addition of fluids, from a nearby igneous intrusion.
  431. igneous rock
    rock formed by the solidification of molten magma
    Crystalline=Rock types made up of crystals or crystal fragments, such as metamorphic rocks that recrystallized in high temperature or pressure environments, or igneous rocks that formed from cooling of a melt.
  432. imbalance
    a lack of balance or state of disequilibrium
    Drought=Abnormal dry weather for a specific area that is sufficiently prolonged for the lack of water to cause serious hydrological imbalance.
  433. impact
    the striking of one body against another
    Abrasion=The mechanical wearing and grinding of rock surfaces by friction and impact.
  434. impermeable
    preventing especially liquids to pass or diffuse through
    Artesian aquifer=An inclined aquifer that is bounded top and bottom by layers of impermeable rock so the water is under pressure.
  435. inclined
    at an angle to the horizontal or vertical position
    Artesian aquifer=An inclined aquifer that is bounded top and bottom by layers of impermeable rock so the water is under pressure.
  436. include
    have as a part, be made up out of
    Andesite minerals commonly include plagioclase and hornblende, with lesser amounts of mica, pyroxene, and various accessory minerals.
  437. indicate
    indicate a place, direction, person, or thing; either spatially or figuratively
    This movement is amplified by a spring or gear mechanism to indicate changes in air pressure on a scale or recording chart.
  438. infinitely
    continuing forever without end
    The big bang theory postulates that 10 to 20 billion years ago, all matter exploded from an infinitely compressed state.
  439. influence
    a power to affect persons or events especially power based on prestige etc
    Continental glacier=A glacier that forms a continuous cover of ice over areas of 50,000 square kilometers or more and spreads outward in all directions under the influence of its own weight. (syn: ice sheet)
    Continental margin=The region between the shoreline of a continent and the deep ocean basins including the continental shelf, continental slope, and continental rise.
  440. inhabit
    inhabit or live in; be an inhabitant of
    Biosphere=The zone inhabited by life.
  441. initial
    occurring at the beginning
    Branching chain reaction=A nuclear fission reaction in which the initial reaction releases two or three neutrons, each of which triggers the fission of additional nuclei.
  442. injection
    the forceful insertion of a substance under pressure
    Recharge could result from reservoirs, storage basins, leaky canals, direct injection of water into an aquifer, or by spreading water over a large land surface.
  443. instrument
    the means whereby some act is accomplished
    Altimeter=An instrument used to determine the altitude of an object with respect to a fixed level.
  444. interact
    act together or towards others or with others
    Cosmic ray=Electromagnetic rays of extremely high frequency and energy; cosmic rays usually interact with the atoms of the atmosphere before reaching the surface of the Earth.
  445. interaction
    a mutual or reciprocal action; interacting
    Aurora borealis=The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.
  446. interior
    inside and toward a center
    The difference between the exterior air pressure and the interior pressure causes the disk to expand or contract slightly.
  447. intermediate
    lying between two extremes in time or space or state
    Andean margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: active continental margin)
    Andesite= Intermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
  448. interplanetary
    between or among planets
    Comet=An interplanetary body composed of loosely bound rock and ice, that forms a bright head and extended fuzzy tail when it enters the inner potion of the solar system.
  449. interstellar
    between or among stars
    Emission nebula=A glowing cloud of interstellar gas.
  450. interval
    the distance between things
    Contour interval=the difference in elevation between two consecutive contour lines
    Contour line=line on a topographic map that connects points on land that have the same elevation.
  451. intrude
    enter uninvited
    Dike=A sheetlike body of igneous rock that cuts across layering or contacts in the rock into which it intrudes.
  452. intrusive
    tending to intrude (especially upon privacy)
    Batholith=A large plutonic mass of intrusive rock with more than 100 square kilometers of surface exposed.
  453. inversion
    the act of turning inside out
    Atmospheric inversion=See "inversion (atmospheric)."
  454. invisible
    impossible or nearly impossible to see; imperceptible by the eye
    Eclipse=A phenomenon that occurs when a heavenly body is shadowed by another and therefore rendered invisible.
  455. ion
    a particle that is electrically charged (positive or negative); an atom or molecule or group that has lost or gained one or more electrons
    Anion=An ion that has a negative charge.
  456. ionized
    converted totally or partly into ions
    Corona=The luminous irregular envelope of highly ionized gas outside the chromosphere of the Sun.
    Correlation=the process of matching rock layers from different locations.
  457. isolated
    remote and separate physically or socially
    Butte=A conspicuous, isolated, flattop hill with steep slopes.
  458. isotope
    one of two or more atoms with the same atomic number but with different numbers of neutrons
    Daughter isotope=An isotope formed by radioactive decay of another isotope.
  459. jagged
    having a sharply uneven surface or outline
    Aa=A lava flow that has a jagged, sharp, broken surface (like glass).
  460. jet
    a hard black form of lignite that takes a brilliant polish and is used in jewelry or ornamentation
    Black smoker=A jet of black water spouting from a fracture in the sea floor, commonly near the mid-oceanic ridge.
  461. jet stream
    a high-speed high-altitude airstream blowing from west to east near the top of the troposphere; has important effects of the formation of weather fronts
    Current=A horizontal movement of water, such as the Gulf Stream off the east coast of North America, or air, such as the jet stream.
  462. Johannes Kepler
    German astronomer who first stated laws of planetary motion (1571-1630)
    Johannes Kepler first discovered that the orbits of the planets are ellipses, not circles; he based his discovery on the careful observations of Tycho Brahe.
  463. Jupiter
    (Roman mythology) supreme god of Romans; counterpart of Greek Zeus
    Asteroid number=Asteroids are assigned a serial number when they are discovered; it has no particular meaning except that asteroid N+1 was discovered after asteroid N.
    Asteroid=One of the many small celestial bodies in orbit around the Sun. Most asteroids orbit between Mars and Jupiter.
  464. Kelvin
    British physicist who invented the Kelvin scale of temperature and pioneered undersea telegraphy (1824-1907)
    The value is 0o Kelvin, -273.15o
  465. Kepler
    German astronomer who first stated laws of planetary motion (1571-1630)
    Johannes Kepler first discovered that the orbits of the planets are ellipses, not circles; he based his discovery on the careful observations of Tycho Brahe.
  466. lagoon
    a body of water cut off from a larger body by a reef of sand or coral
    Atoll=A circular reef that surrounds a lagoon and is bounded on the outside by deep water of the open sea.
  467. lahar
    an avalanche of volcanic water and mud down the slopes of a volcano
    Debris Flow=A mixture of water-saturated rock debris that flows downslope under the force of gravity (also called lahar or mudflow).
  468. land mass
    a large continuous extent of land
    Accreted terrain=A land mass that originated as an island arc or a microcontinent that was later added onto a continent.
  469. landslide
    an overwhelming electoral victory
    Some common types of erosion includes landslides, rockfalls, creep, etc.
  470. lapse
    drop to a lower level, as in one's morals or standards
    Dry adiabatic lapse rate=The rate of cooling that occurs when dry air rises without gain or loss of heat.
  471. lava
    rock that in its molten form (as magma) issues from volcanos; lava is what magma is called when it reaches the surface
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  472. layer
    single thickness of usually some homogeneous substance
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  473. layered
    with one layer on top of another
    Banded iron formation=Iron-rich layered sedimentary rocks precipitated from the seas mostly between 2.6 and 1.9 billion years ago, as a result of rising atmospheric oxygen concentrations.
  474. leach
    cause (a liquid) to leach or percolate
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  475. leading edge
    forward edge of an airfoil
    Cold front=the leading edge of an advancing cold air mass that is under running and displacing the warmer air in its path.
  476. levee
    an embankment that is built in order to prevent a river from overflowing
    Artificial levee=A wall built along the banks of a stream to prevent rising flood water from spilling out of the stream channel onto the flood plain.
  477. level
    a relative position or degree of value in a graded group
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  478. liberation
    the act of liberating someone or something
    Results in liberation of 80 calories per cubic centimeter.
  479. light year
    the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers
    Absolute magnitude=The brightness that a star would appear to have if it were 32 light-years (10 parsecs) away.
  480. light-year
    the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers
    Absolute magnitude=The brightness that a star would appear to have if it were 32 light-years (10 parsecs) away.
  481. linkage
    the act of linking things together
    Chemical bond=The linkage between atoms in molecules and between molecules and ions in crystals.
  482. liquid
    fluid matter having no fixed shape but a fixed volume
    Aneroid means "without liquid."
  483. lithosphere
    the solid part of the earth consisting of the crust and outer mantle
    Asthenosphere=The portion of the upper mantle beneath the lithosphere.
  484. location
    the act of putting something in a certain place
    Climate=typical weather patterns over a period of years in a given location
    Climate=The composite pattern of long-term weather conditions that can be expected in a given region.
  485. low density
    a rarified quality
    Continental climate=large yearly temperature ranges
    Continental Crust=Solid, outer layers of the earth, including the rocks of the continents; thick, low density, granitic, and old.
  486. low frequency
    30 to 300 kilohertz
    Electromagnetic spectrum=The entire range of electromagnetic radiation from very long wavelength ( low frequency) radiation to very short wavelength (high frequency) radiation.
  487. low-grade
    of inferior quality
    Disseminated ore deposit=A large low-grade ore deposit in which generally fine-grained metal-bearing minerals are widely scattered throughout a rock body in sufficient concentration to make the deposit economical to mine.
  488. luminous
    softly bright or radiant
    Corona=The luminous irregular envelope of highly ionized gas outside the chromosphere of the Sun.
    Correlation=the process of matching rock layers from different locations.
  489. lunar
    of or relating to or associated with the moon
    When the Earth lies directly between the Sun and the Moon, the Earth's shadow falls on the Moon and we observe a lunar eclipse.
  490. lunar eclipse
    the earth interrupts light shining on the moon
    When the Earth lies directly between the Sun and the Moon, the Earth's shadow falls on the Moon and we observe a lunar eclipse.
  491. magma
    molten rock in the earth's crust
    By far the most common variety is vitric ash (glassy particles formed by gas bubbles bursting through liquid magma).
  492. magnesium
    a light silver-white ductile bivalent metallic element; in pure form it burns with brilliant white flame; occurs naturally only in combination (as in magnesite and dolomite and carnallite and spinel and olivine)
    Andean margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: active continental margin)
    Andesite=Intermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
  493. magnetic
    of or relating to or caused by magnetism
    Aurora borealis=The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.
  494. magnetic field
    the lines of force surrounding a permanent magnet or a moving charged particle
    Aurora borealis=The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.
  495. magnetism
    attraction for iron; associated with electric currents as well as magnets; characterized by fields of force
    Curie point=The temperature below which rocks can retain magnetism.
  496. magnitude
    the property of relative size or extent (whether large or small)
    Absolute magnitude=The brightness that a star would appear to have if it were 32 light-years (10 parsecs) away.
  497. major
    greater in scope or effect
    Blizzard=Although blizzard is often used to describe any major snow storm with strong winds, the technical definition for a blizzard requires at least 3 hours in duration; low temperatures (usually less than minus 7C or 20F), strong winds (greater than 55 km/h or 35 mph), blowing snow which reduces visibility to less that 1 kilometer (0.6 miles).
  498. mar
    make imperfect
    Asteroid number=Asteroids are assigned a serial number when they are discovered; it has no particular meaning except that asteroid N+1 was discovered after asteroid N.
    Asteroid=One of the many small celestial bodies in orbit around the Sun. Most asteroids orbit between Mars and Jupiter.
  499. margin
    the boundary line or the area immediately inside the boundary
    Active continental margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: Andean margin)
    Active volcano=A volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
  500. marine
    of or relating to the sea
    Chalk=A very fine grained, soft, earthy, white to gray bioclastic limestone made of the shells and skeletons of marine microorganisms.
  501. Mars
    (Roman mythology) Roman god of war and agriculture; father of Romulus and Remus; counterpart of Greek Ares
    Asteroid number=Asteroids are assigned a serial number when they are discovered; it has no particular meaning except that asteroid N+1 was discovered after asteroid N.
    Asteroid=One of the many small celestial bodies in orbit around the Sun. Most asteroids orbit between Mars and Jupiter.
  502. matrix
    an enclosure within which something originates or develops (from the Latin for womb)
    Breccia=A course-grained rock, composed of angular, broken rock fragments held together by a mineral cement or a fine-grained matrix.
  503. maximum
    the greatest or most complete or best possible
    Angle of repose=The maximum slope or angle at which loose material remains stable.
  504. measure
    determine the measurements of something or somebody, take measurements of
    The type normally used by meteorologists measures the altitude with respect to sea level pressure.
  505. mechanical
    using (or as if using) mechanisms or tools or devices
    Abrasion=The mechanical wearing and grinding of rock surfaces by friction and impact.
  506. mechanism
    device consisting of a piece of machinery; has moving parts that perform some function
    This movement is amplified by a spring or gear mechanism to indicate changes in air pressure on a scale or recording chart.
  507. melt
    reduce or cause to be reduced from a solid to a liquid state, usually by heating
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  508. meltwater
    melted snow or ice
    Drift=(glacial) Any rock or sediment transported and deposited by a glacier or by glacial meltwater.
  509. mercury
    a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures
    There are three common types of barometers used widely today: mercury barometer; aneroid barometer; electronic barometer.
  510. mesa
    flat tableland with steep edges
    A butte is smaller and more tower-like than a mesa.
  511. mesosphere
    the atmospheric layer between the stratosphere and the thermosphere
    The most common layer designations are: the troposphere, the stratosphere, the mesosphere and the exosphere.
  512. Mesozoic
    of or relating to or denoting the Mesozoic era
    Cretaceous-Tertiary boundary=A major stratigraphic boundary on Earth marking the end of the Mesozoic Era, best known as the age of the dinosaurs.
  513. metal
    any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
    The black color is caused by precipitation of very fine grained metal sulfide minerals as hydrothermal solutions cool by contact with sea water.
  514. metamorphic
    of or relating to metamorphosis (especially of rocks)
    Basement rock=The older granitic and related metamorphic rocks of the Earth's crust that make up the foundations of continents.
  515. metamorphic rock
    rock altered by pressure and heat
    Basement rock=The older granitic and related metamorphic rocks of the Earth's crust that make up the foundations of continents.
  516. metamorphism
    change in the structure of rock by natural agencies such as pressure or heat or introduction of new chemical substances
    Burial metamorphism=Metamorphism that results from deep burial of rocks in a sedimentary basin.
  517. meteorite
    stony or metallic object that is the remains of a meteoroid that has reached the earth's surface
    The boiling point of pure water at standard pressure is 100°C or 212°F.
    Bolide=An exploding meteorite.
  518. meteorology
    the earth science dealing with phenomena of the atmosphere (especially weather)
    Advection=In meteorology, the horizontal component of a convection current in air, i.e.
  519. meter
    the basic unit of length adopted under the Systeme International d'Unites (approximately 1.094 yards)
    Absolute Humidity=The ratio of the mass of water vapor present in the air to the volume occupied by the gas; the density of water vapor in the air, usually expressed as grams of water vapor per cubic meter of air.
  520. microcrystalline
    containing crystals that are visible only under a microscope
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  521. microorganism
    any organism of microscopic size
    Bioremediation=The use of microorganisms to decompose an environmental contaminant.
  522. millibar
    a unit of atmospheric pressure equal to one thousandth of a bar
    One is in millibars.
  523. mineral
    solid homogeneous inorganic substances occurring in nature having a definite chemical composition
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  524. modified
    changed in form or character
    Because of their semi-plastic condition, bombs are often modified in shape during their flight or upon impact.
  525. modify
    cause to change; make different; cause a transformation
    Artificial channel=Any channel dredged to modify the natural channel or to alter the course of a stream.
  526. moisture
    wetness caused by water
    Dew= Moisture condensed onto objects from the atmosphere, usually during the night, when the ground and leaf surfaces become cooler than the surrounding air.
  527. molecular
    relating to or produced by or consisting of molecules
    Absolute Zero=Considered to be the point at which theoretically no molecular activity exists or the temperature at which the volume of a perfect gas vanishes.
  528. molecule
    (physics and chemistry) the simplest structural unit of an element or compound
    Aerosol=Any small particle that is larger than a molecule and suspended in air.
  529. molten
    reduced to liquid form by heating
    Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted.
  530. Moon
    the natural satellite of the Earth
    Aristotle postulated that the Sun, Moon, planets, and stars are imbedded in the spheres.
  531. moraine
    accumulated earth and stones deposited by a glacier
    End moraine=A moraine that forms at the end, or terminus of a glacier.
  532. motion
    the act of changing location from one place to another
    Conduction=The transport of heat by atomic or molecular motion.
  533. muddy
    (of soil) soft and watery
    Carbonate platform=An extensive accumulation of limestone such as the Florida Keys and the Bahamas, formed on a continental shelf in warm regions where sediment does not muddy the water and reef-building organisms thrive.
  534. narrow
    not wide
    The oldest known rocks formed at the beginning of or just prior to the start of the Archean Eon.
    Arête=A sharp narrow ridge between adjacent valleys formed by glacial erosion.
  535. natural gas
    a fossil fuel in the gaseous state; used for cooking and heating homes
    Energy resources=Geologic resources, including petroleum, coal, natural gas, and nuclear fuels, used for heat, light, work, and communication.
  536. nebula
    an immense cloud of gas (mainly hydrogen) and dust in interstellar space
    Absorption nebula=A cold nebula that absorbs light.
  537. negative
    characterized by or displaying negation or denial or opposition or resistance; having no positive features
    Anion=An ion that has a negative charge.
  538. negative charge
    having a surplus of electrons; having a lower electric potential
    Anion=An ion that has a negative charge.
  539. net
    an open fabric of string or rope or wire woven together at regular intervals
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  540. neutron
    an elementary particle with 0 charge and mass about equal to a proton; enters into the structure of the atomic nucleus
    Branching chain reaction=A nuclear fission reaction in which the initial reaction releases two or three neutrons, each of which triggers the fission of additional nuclei.
  541. newton
    a unit of force equal to the force that imparts an acceleration of 1 m/sec/sec to a mass of 1 kilogram; equal to 100,000 dynes
    Atmosphere=One atmosphere is 14.7 pounds per square inch (105 Newtons per square meter); the average atmospheric pressure at sea level on Earth.
  542. nickel
    a hard malleable ductile silvery metallic element that is resistant to corrosion; used in alloys; occurs in pentlandite and smaltite and garnierite and millerite
    Core, inner=spherical center of the Earth, about 1200 km in diameter and made of solid iron and nickel.
  543. nitrate
    any compound containing the nitrate group (such as a salt or ester of nitric acid)
    Eutrophic lake=A lake characterized by abundant dissolved nitrates, phosphates, and other plant nutrients and by a seasonal deficiency of oxygen in bottom water.
  544. nitrogen
    a common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living tissues
    The principal gases that compose dry air are Nitrogen (N2) 78.09%;
  545. normally
    under normal conditions
    The type normally used by meteorologists measures the altitude with respect to sea level pressure.
  546. northern lights
    the aurora of the northern hemisphere
    Aurora borealis=The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.
  547. nuclear
    constituting or like a nucleus
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  548. nuclear fission
    a nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  549. nuclear fuel
    fuel (such as uranium) that can be used in nuclear reactors as a source of electricity
    Energy resources=Geologic resources, including petroleum, coal, natural gas, and nuclear fuels, used for heat, light, work, and communication.
  550. nuclear fusion
    a nuclear reaction in which nuclei combine to form more massive nuclei with the simultaneous release of energy
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  551. nucleus
    a part of the cell containing DNA and RNA and responsible for growth and reproduction
    Branching chain reaction=A nuclear fission reaction in which the initial reaction releases two or three neutrons, each of which triggers the fission of additional nuclei.
  552. nutrient
    any substance that can be metabolized by an animal to give energy and build tissue
    Eutrophic lake=A lake characterized by abundant dissolved nitrates, phosphates, and other plant nutrients and by a seasonal deficiency of oxygen in bottom water.
  553. object
    a tangible and visible entity; an entity that can cast a shadow
    Albedo=Reflectivity of an object; ratio of reflected light to incident light.
  554. observe
    watch attentively
    When the Moon lies directly between the Earth and the Sun, the Moon blocks our view of the Sun and we observe a solar eclipse.
  555. occur
    come to pass
    Adiabatic temperature changes=Temperature changes that occur without gain or loss of heat.
  556. ocean floor
    the bottom of a sea or ocean
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  557. oceanic
    relating to or occurring or living in or frequenting the open ocean
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid- oceanic ridge and the continental rise.
  558. opposite
    being directly across from each other; facing
    Anticyclonic=The wind circulation pattern in Highs, or anticyclones, that has a sense of rotation opposite to that of cyclones and the Earth's rotation.
  559. orbit
    the (usually elliptical) path described by one celestial body in its revolution about another
    Aphelion =The point in its orbit where a planet is farthest from the Sun.
    Apogee =The point in orbit farthest from the Earth.
  560. ore
    a mineral that contains metal that is valuable enough to be mined
    It is the principle ore of aluminum.
  561. organic
    being or relating to or derived from or having properties characteristic of living organisms
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  562. organism
    a living thing that has (or can develop) the ability to act or function independently
    Bioclastic sedimentary rock=Sedimentary rocks such as most limestone, that are composed of broken shell fragments and similar remains of living organisms.
  563. orientation
    the act of orienting
    Aspect=The orientation of a slope with respect to the Sun; the geographic orientation or exposure of a slope.
  564. orifice
    an aperture or hole that opens into a bodily cavity
    Crater=A depression formed by the impact of a meteorite. 2) A depression around the orifice of a volcano.
  565. oxide
    any compound of oxygen with another element or a radical
    Bauxite=A gray, yellow, or reddish brown rock composed of a mixture of aluminum oxides and hydroxides.
  566. oxygen
    a nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust
    Oxygen (O2) 20.946%;
  567. ozone
    a colorless gas (O3) soluble in alkalis and cold water; a strong oxidizing agent; can be produced by electric discharge in oxygen or by the action of ultraviolet radiation on oxygen in the stratosphere (where it acts as a screen for ultraviolet radiation)
    Antarctic Ozone Hole=An extended area of extreme depletion of the ozone layer which forms over the southern polar region eachaustral spring (September through November).
  568. ozone hole
    an area of the ozone layer (near the poles) that is seasonally depleted of ozone
    Antarctic Ozone Hole=An extended area of extreme depletion of the ozone layer which forms over the southern polar region eachaustral spring (September through November).
  569. ozone layer
    a layer in the stratosphere (at approximately 20 miles) that contains a concentration of ozone sufficient to block most ultraviolet radiation from the sun
    Antarctic Ozone Hole=An extended area of extreme depletion of the ozone layer which forms over the southern polar region eachaustral spring (September through November).
  570. pahoehoe
    freely flowing lava
    Aa flows commonly developed from pahoehoe flows as they cool and lose gas.
  571. parallel
    being everywhere equidistant and not intersecting
    Barrier island=A long, narrow, low-lying island that extends parallel to the shoreline.
  572. parsec
    a unit of astronomical length based on the distance from Earth at which stellar parallax is 1 second of arc; equivalent to 3.262 light years
    Absolute magnitude=The brightness that a star would appear to have if it were 32 light-years (10 parsecs) away.
  573. particle
    (nontechnical usage) a tiny piece of anything
    Aerosol=Any small particle that is larger than a molecule and suspended in air.
  574. pascal
    a unit of pressure equal to one newton per square meter
    Bar=A unit of pressure, equal to the sea-level pressure of Earth's atmosphere; 1 bar = 0.987 atmosphere = 101,300 pascals = 14.5 lbs/square inch = 100,000 Newtons per square meter.
  575. passive
    lacking in energy or will
    Usually, the continental shelf will be wider along a passive continental margin, and narrower along an active margin.
  576. pattern
    a perceptual structure
    In the northern hemisphere, the Coriolis effect deflects the diverging winds to the right, forming a pinwheel pattern with the air spiraling clockwise.
  577. percent
    a proportion in relation to a whole (which is usually the amount per hundred)
    Andean margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: active continental margin)
    Andesite=Intermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
  578. perfect gas
    a hypothetical gas with molecules of negligible size that exert no intermolecular forces
    Absolute Zero=Considered to be the point at which theoretically no molecular activity exists or the temperature at which the volume of a perfect gas vanishes.
  579. period
    an amount of time
    Climate=typical weather patterns over a period of years in a given location
    Climate=The composite pattern of long-term weather conditions that can be expected in a given region.
  580. periodically
    in a sporadic manner
    Crystal=A solid element or compound whose atoms are arranged in a regular, orderly, periodically repeated array.
  581. permeable
    allowing fluids or gases to pass or diffuse through
    Aquifer=A porous and permeable body of rock that can yield economically significant quantities of ground water.
  582. petroleum
    a dark oil consisting mainly of hydrocarbons
    Petroleum, asphalt, natural mineral wax, and asphaltites are all bitumens.
  583. Phanerozoic
    the period from about 5,400 million years ago until the present
    The most recent eon, the Phanerozoic Eon, is further subdivided into eras.
  584. phase
    any distinct time period in a sequence of events
    Condensation=The change of state of water from the vapor to the liquid phase.
  585. phosphate
    a salt of phosphoric acid
    Eutrophic lake=A lake characterized by abundant dissolved nitrates, phosphates, and other plant nutrients and by a seasonal deficiency of oxygen in bottom water.
  586. photosphere
    the intensely luminous surface of a star (especially the sun)
    Chromosphere=A turbulent diffuse gaseous layer of the Sun that lies above the photosphere.
  587. physic
    a purging medicine; stimulates evacuation of the bowels
    Energy=Usable heat or power; in physics, it is the capacity of a physical system to perform work.
  588. physicist
    a scientist trained in physics
    Named for J. Christian Doppler, an Austrian physicist, who in 1842 explained why the whistle of an approaching train had a higher pitch than the same whistle when the train was going away.
  589. physics
    the science of matter and energy and their interactions
    Energy=Usable heat or power; in physics, it is the capacity of a physical system to perform work.
  590. pinwheel
    a toy consisting of vanes of colored paper or plastic that is pinned to a stick and spins when it is pointed into the wind
    In the northern hemisphere, the Coriolis effect deflects the diverging winds to the right, forming a pinwheel pattern with the air spiraling clockwise.
  591. plain
    not elaborate or elaborated; simple
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  592. planet
    (astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise direction
    Aphelion =The point in its orbit where a planet is farthest from the Sun.
    Apogee =The point in orbit farthest from the Earth.
  593. planetary
    of or relating to or resembling the physical or orbital characteristics of a planet or the planets
    Eccentricity=A value that defines the shape of an ellipse or planetary orbit; the ratio of the distance between the foci and the major axis.
  594. plate tectonics
    the branch of geology studying the folding and faulting of the earth's crust
    The continental drift theory has been replaced by the more complete plate tectonics theory.
  595. plutonic
    of igneous rock that has solidified beneath the earth's surface; granite or diorite or gabbro
    Batholith=A large plutonic mass of intrusive rock with more than 100 square kilometers of surface exposed.
  596. polar
    of or existing at or near a geographical pole or within the Arctic or Antarctic Circles
    Antarctic Ozone Hole=An extended area of extreme depletion of the ozone layer which forms over the southern polar region eachaustral spring (September through November).
  597. pollution
    undesirable state of the natural environment being contaminated with harmful substances as a consequence of human activities
    Cost benefit analysis=A system of analysis that attempts to weigh the cost of an act or policy, such as pollution control, directly against the economic benefits.
  598. pore
    any tiny hole admitting passage of a liquid (fluid or gas)
    Capillary action=The action by which water is pulled upward through small pores by electrical attraction to the pore walls.
  599. porous
    full of pores or vessels or holes
    Aquifer=A porous and permeable body of rock that can yield economically significant quantities of ground water.
  600. portion
    something determined in relation to something that includes it
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  601. positively
    so as to be positive; in a positive manner
    Cation=A positively charged ion.
  602. positively charged
    having a positive charge
    Cation=A positively charged ion.
  603. postulate
    maintain or assert
    The big bang theory postulates that 10 to 20 billion years ago, all matter exploded from an infinitely compressed state.
  604. potion
    a medicinal or magical or poisonous beverage
    Comet=An interplanetary body composed of loosely bound rock and ice, that forms a bright head and extended fuzzy tail when it enters the inner potion of the solar system.
  605. precipitate
    bring about abruptly
    Caliche=A hard soil layer formed when calcium carbonate precipitates and cements the soil.
  606. precipitation
    the falling to earth of any form of water (rain or snow or hail or sleet or mist)
    Acid precipitation=A condition in which natural precipitation becomes acidic after reacting with air pollutants.
  607. predominantly
    much greater in number or influence
    Claystone=A fine-grained clastic sedimentary rock composed predominantly of clay minerals and small amounts of quartz and other minerals of clay size.
  608. present
    temporal sense; intermediate between past and future; now existing or happening or in consideration
    Absolute Humidity=The ratio of the mass of water vapor present in the air to the volume occupied by the gas; the density of water vapor in the air, usually expressed as grams of water vapor per cubic meter of air.
  609. primarily
    for the most part
    Carbonate rocks=Rocks such as limestone and dolomite made up primarily of carbonate minerals.
  610. principal
    most important element
    The principal gases that compose dry air are Nitrogen (N2) 78.09%;
  611. prior
    earlier in time
    The oldest known rocks formed at the beginning of or just prior to the start of the Archean Eon.
    Arête=A sharp narrow ridge between adjacent valleys formed by glacial erosion.
  612. process
    a particular course of action intended to achieve a result
    Calving=A process in which large chunks of ice break off from tidewater glaciers to form icebergs.
  613. projected
    extending out above or beyond a surface or boundary
    Disk=The visible surface of the Sun (or any heavenly body) projected against the sky.
  614. prolong
    lengthen in time; cause to be or last longer
    Drought=Abnormal dry weather for a specific area that is sufficiently prolonged for the lack of water to cause serious hydrological imbalance.
  615. psychrometer
    a hygrometer consisting of a dry-bulb thermometer and a wet-bulb thermometer; their difference indicates the dryness of the surrounding air
    One of the two thermometers that make up a psychrometer.
  616. Ptolemy
    Alexandrian astronomer (of the 2nd century) who proposed a geocentric system of astronomy that was undisputed until the late Renaissance
    Epicycle=a small orbit along which a planet traveled in Ptolemy's geocentric model of the solar system.
  617. radar
    measuring instrument in which the echo of a pulse of microwave radiation is used to detect and locate distant objects
    Doppler Radar=Weather radar that measures direction and speed of a moving object, such as drops of precipitation, by determining whether atmospheric motion is horizontally toward or away from the radar.
  618. radiation
    the act of spreading outward from a central source
    Electromagnetic radiation=The transfer of energy by an oscillating electric and magnetic field; it travels as a wave and also behaves as a stream of particles.
  619. radiator
    any object that radiates energy
    Blackbody temperature=The temperature of an object if it is reradiating all the thermal energy that has been added to it; if an object is not a blackbody radiator, it will not reradiate all the excess heat and the leftover will go toward increasing its temperature.
  620. radio wave
    an electromagnetic wave with a wavelength between 0.5 cm to 30,000 m
    Electromagnetic spectrum=total range of electromagnetic waves, from radio waves to gamma waves.
  621. radioactive
    exhibiting or caused by radioactivity
    Absolute Date=An estimate of the true age of a mineral or rock based on the rate of decay of radioactive minerals.
  622. radioactive decay
    the spontaneous disintegration of a radioactive substance along with the emission of ionizing radiation
    Daughter isotope=An isotope formed by radioactive decay of another isotope.
  623. rainfall
    water falling in drops from vapor condensed in the atmosphere
    Climate refers to yearly cycles of temperature, wind, rainfall, etc., and not to daily variations (see "weather").
  624. rainstorm
    a storm with rain
    Local squalls and rainstorms are common, and steady winds are rare.
  625. range
    a variety of different things or activities
    Cobbles=Rounded rock fragments in the 64 to 256 mm size range, larger than pebbles and smaller than boulders.
  626. ranging
    wandering freely
    Also the thinnest layer in sedimentary rocks, commonly ranging in thickness from a centimeter to a meter or two.
  627. rapid
    characterized by speed; moving with or capable of moving with high speed
    Debris Avalanche=A rapid and unusually sudden sliding or flowage of unsorted masses of rock and other material.
  628. rare
    marked by an uncommon quality; especially superlative or extreme of its kind
    Catastrophism=The model that Earth change occurs through a series of rare but cataclysmic events.
  629. rate
    a quantity or amount or measure considered as a proportion of another quantity or amount or measure
    Absolute Date=An estimate of the true age of a mineral or rock based on the rate of decay of radioactive minerals.
  630. ratio
    the relation between things (or parts of things) with respect to their comparative quantity, magnitude, or degree
    Absolute Humidity=The ratio of the mass of water vapor present in the air to the volume occupied by the gas; the density of water vapor in the air, usually expressed as grams of water vapor per cubic meter of air.
  631. react
    show a response or a reaction to something
    Acid precipitation=A condition in which natural precipitation becomes acidic after reacting with air pollutants.
  632. reaction
    an idea evoked by some experience
    Branching chain reaction=A nuclear fission reaction in which the initial reaction releases two or three neutrons, each of which triggers the fission of additional nuclei.
  633. reactor
    (physics) any of several kinds of apparatus that maintain and control a nuclear reaction for the production of energy or artificial elements
    Control rod=A column of neutron-absorbing alloys that are spaced among fuel rods to fine-tune nuclear fission in a reactor.
  634. recent
    of the immediate past or just previous to the present time
    Active continental margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: Andean margin)
    Active volcano=A volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
  635. recharge
    charge anew
    Artificial Recharge=The unnatural addition of surface waters to groundwater.
  636. record
    anything (such as a document or a phonograph record or a photograph) providing permanent evidence of or information about past events
    This movement is amplified by a spring or gear mechanism to indicate changes in air pressure on a scale or recording chart.
  637. reduce
    make smaller
    Often these snow storms have high winds reaching 100 km/h which reduce visibility through blowing and drifting snow.
  638. reflect
    to throw or bend back (from a surface)
    Albedo=Reflectivity of an object; ratio of reflected light to incident light.
  639. reflectivity
    the capability of quiet thought or contemplation
    Albedo= Reflectivity of an object; ratio of reflected light to incident light.
  640. region
    the extended spatial location of something
    Alberta Clipper=A fast moving winter storm originating in the Alberta, Canada region.
  641. relative humidity
    the ratio of the amount of water in the air at a give temperature to the maximum amount it could hold at that temperature; expressed as a percentage
    Dew point=The temperature at which the relative humidity of air reaches 100 percent, and the air becomes saturated.
  642. relativity
    the quality of being relative and having significance only in relation to something else
    E=mc2 Einstein's famous theory of relativity formula known as the energy-mass relation.
  643. release
    grant freedom to; free from confinement
    Branching chain reaction=A nuclear fission reaction in which the initial reaction releases two or three neutrons, each of which triggers the fission of additional nuclei.
  644. removal
    the act of removing
    Erosion=The removal of weathered rocks by moving water, wind, ice, or gravity.
  645. removed
    separate or apart in time
    Elastic deformation=A deformation such that if the stress is removed, the material springs back to its original size and shape.
  646. repose
    freedom from activity (work or strain or responsibility)
    Angle of repose=The maximum slope or angle at which loose material remains stable.
  647. resemble
    appear like; be similar or bear a likeness to
    Anticline=A fold in rock that resembles an arch; the fold is convex upward and the oldest rocks are in the middle Anticyclone: An area of high pressure, also called a High, around which the winds circulate in a clockwise direction in the Northern Hemisphere (and counterclockwise in the Southern Hemisphere).
  648. resource
    a source of aid or support that may be drawn upon when needed
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  649. respect
    regard highly; think much of
    Altimeter=An instrument used to determine the altitude of an object with respect to a fixed level.
  650. retrograde
    moving or directed or tending in a backward direction or contrary to a previous direction
    They were created to explain retrograde motion.
  651. reverse
    change to the contrary
    Equinox=The date when the sun is directly overhead at noon on the equator, occurring on or around both March 21 and September 22, the former is the vernal (spring) equinox and the latter the autumnal (fall) equinox in the Northern Hemisphere and the reverse on the Southern Hemisphere.
  652. rock salt
    naturally occurring crystalline sodium chloride
    Chemical sedimentary rock=Rocks such as rock salt, that form by direct precipitation of minerals from solution.
  653. rod
    a long thin implement made of metal or wood
    Control rod=A column of neutron-absorbing alloys that are spaced among fuel rods to fine-tune nuclear fission in a reactor.
  654. rotate
    turn on or around an axis or a center
    Axis of rotation=An imaginary straight line through a planet's poles on which the planet rotates.
  655. rotation
    the act of rotating as if on an axis
    Anticyclonic=The wind circulation pattern in Highs, or anticyclones, that has a sense of rotation opposite to that of cyclones and the Earth's rotation.
  656. rupture
    the act of making a sudden noisy break
    Brittle fracture= Rupture that occurs when a rock breaks sharply.
  657. saturated
    being the most concentrated solution possible at a given temperature; unable to dissolve still more of a substance
    Debris Flow=A mixture of water- saturated rock debris that flows downslope under the force of gravity (also called lahar or mudflow).
  658. saturation
    the process of totally saturating something with a substance
    Condensation Level=The altitude at which a rising air parcel reaches saturation, usually the cloud base height.
  659. scale
    an ordered reference standard
    Altimeter=A barometer with a scale calibrated in units of elevation rather than pressure.
  660. sea floor
    the bottom of a sea or ocean
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep- sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  661. sea level
    level of the ocean's surface (especially that halfway between mean high and low tide); used as a standard in reckoning land elevation or sea depth
    The type normally used by meteorologists measures the altitude with respect to sea level pressure.
  662. sediment
    matter that has been deposited by some natural process
    Abyssal fan=A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  663. sedimentary
    resembling or containing or formed by the accumulation of sediment
    Angular unconformity=An unconformity in which younger sediment or sedimentary rocks rest on the eroded surface of tilted orfolded older rocks.
  664. sedimentary rock
    rock formed from consolidated clay sediments
    Angular unconformity=An unconformity in which younger sediment or sedimentary rocks rest on the eroded surface of tilted orfolded older rocks.
  665. seismic
    subject to or caused by an earthquake or earth vibration
    Blue stars=These are the hottest stars, with a surface temperature of more than 37,000°F.
    Body wave=A seismic wave that travel through the interior of the Earth.
  666. semiarid
    somewhat arid
    Desertification=A process by which semiarid land is converted to desert, often by improper farming or by climate change.
  667. sensor
    any device that receives a signal or stimulus (as heat or pressure or light or motion etc.) and responds to it in a distinctive manner
    Anemometer=an instrument that measures wind speed
    Aneriod Barometer=A barometer whose pressure sensor consists of an aneroid capsule, a thin, hollow disk partially evacuated and sealed.
  668. separate
    standing apart; not attached to or supported by anything
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  669. series
    similar things placed in order or happening one after another
    Catastrophism=The model that Earth change occurs through a series of rare but cataclysmic events.
  670. several
    (used with count nouns) of an indefinite number more than 2 or 3 but not many
    Asteroid=A rocky space object that can be from a few hundred feet to several hundred km wide.
  671. shallow
    lacking physical depth; having little spatial extension downward or inward from an outer surface or backward or outward from a center
    Braided stream=A stream that divides into a network of branching and reuniting shallow channels separated by mid-channel bars.
  672. shape
    a perceptual structure
    Abyssal fan=A large, fan- shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: submarine fan)
    Abyssal plain=A flat, level, largely featureless part of the ocean floor between the mid-oceanic ridge and the continental rise.
  673. shoreline
    a boundary line between land and water
    Barrier island=A long, narrow, low-lying island that extends parallel to the shoreline.
  674. sickness
    impairment of normal physiological function affecting part or all of an organism
    Epidemiology=The study of the distribution of sickness in a population.
  675. significant
    rich in significance or implication
    Aquifer=A body of rock that contains significant quantities of water that can be tapped by wells or springs.
  676. signified
    the meaning of a word or expression; the way in which a word or expression or situation can be interpreted
    It is a secondary characteristic of an air mass classification, signified by the small "c" before the primary characteristic, which is based on source region.
  677. signify
    denote or connote
    It is a secondary characteristic of an air mass classification, signified by the small "c" before the primary characteristic, which is based on source region.
  678. silica
    a white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earth's crust as quartz or cristobalite or tridymite or lechatelierite
    Andean margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: active continental margin)
    Andesite=Intermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
  679. silicate
    a salt or ester derived from silicic acid
    Amphibole=A group of double chain silicate minerals.
  680. silt
    mud or clay or small rocks deposited by a river or lake
    Alluvium=A general term for clay, silt, sand, gravel or similar unconsolidated material deposited by a stream or other body of running water.
  681. similar
    having the same or similar characteristics
    Alluvium=A general term for clay, silt, sand, gravel or similar unconsolidated material deposited by a stream or other body of running water.
  682. sink
    fall or descend to a lower place or level
    Hot fluids rise, cold fluids sink.
  683. skeleton
    the hard structure (bones and cartilages) that provides a frame for the body of an animal
    Chalk=A very fine grained, soft, earthy, white to gray bioclastic limestone made of the shells and skeletons of marine microorganisms.
  684. slope
    be at an angle
    Angle of repose=The maximum slope or angle at which loose material remains stable.
  685. snowfall
    precipitation falling from clouds in the form of ice crystals
    Surprisingly, snowfall need not be falling as long as the amount of snow in the air (falling or blowing) reduces visibility to less than 400m (0.25 miles).
  686. soil
    material in the top layer of the surface of the earth in which plants can grow (especially with reference to its quality or use)
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  687. solar
    relating to or derived from the sun or utilizing the energies of the sun
    Alpha Centauri=The closest bright star to our solar system.
  688. solar eclipse
    the moon interrupts light from the sun
    Our Sun's corona can only be seen during a total solar eclipse.
  689. solar energy
    energy from the sun that is converted into thermal or electrical energy
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  690. solar system
    the sun with the celestial bodies that revolve around it in its gravitational field
    Alpha Centauri=The closest bright star to our solar system.
  691. solar wind
    a stream of protons moving radially from the sun
    Aurora borealis=The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.
  692. solid
    not soft or yielding to pressure
    Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted.
  693. soluble
    (of a substance) capable of being dissolved in some solvent (usually water)
    Bitumen=A general name for solid and semi-solid hydrocarbons that are fusible and soluble in carbon bisulfide.
  694. solution
    a homogeneous mixture of two or more substances; frequently (but not necessarily) a liquid solution
    The black color is caused by precipitation of very fine grained metal sulfide minerals as hydrothermal solutions cool by contact with sea water.
  695. sound wave
    (acoustics) a wave that transmits sound
    Eccentricity=The shape of the ellipse that constitutes the Earth's orbit around the Sun.
    Echo sounder=An instrument that emits sound waves and then records them after they reflects off the sea floor.
  696. source
    the place where something begins, where it springs into being
    Consumption=Any process that uses water, and then returns it to the Earth far from its source.
  697. span
    the distance or interval between two points
    Devonian=A period of time in the Paleozoic Era that covered the time span between 408 and 360 million years.
  698. sparse
    not dense
    Also defined as a region that supports only a sparse plant cover.
  699. specific
    stated explicitly or in detail
    Absolute dating=A technique that geologists use to assign specific dates to rock formations and geologic events.
  700. spectrum
    a broad range of related objects or values or qualities or ideas or activities
    Absorption spectrum=See "spectrum."
  701. speed of light
    the speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second
    Black hole=An object whose gravity is so strong that the escape velocity exceeds the speed of light.
  702. sphere
    a three-dimensional closed surface such that every point on the surface is equidistant from the center
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  703. spherical
    of or relating to spheres or resembling a sphere
    Core, inner= spherical center of the Earth, about 1200 km in diameter and made of solid iron and nickel.
  704. split
    separate into parts or portions
    Cleavage=The way crystalline minerals split or break along an even plane (planar surfaces).
  705. spring
    move forward by leaps and bounds
    This movement is amplified by a spring or gear mechanism to indicate changes in air pressure on a scale or recording chart.
  706. spring equinox
    March 21
    Equinox=The date when the sun is directly overhead at noon on the equator, occurring on or around both March 21 and September 22, the former is the vernal ( spring) equinox and the latter the autumnal (fall) equinox in the Northern Hemisphere and the reverse on the Southern Hemisphere.
  707. squall
    utter a sudden loud cry
    Precipitation is generally at and/or behind the front, and with a fast-moving system, a squall line may develop ahead of the front.
  708. squall line
    a cold front along which squalls or thunderstorms are likely
    Precipitation is generally at and/or behind the front, and with a fast-moving system, a squall line may develop ahead of the front.
  709. stalactite
    a cylinder of calcium carbonate hanging from the roof of a limestone cave
    Column=A dripstone or speleothem formed when a stalactite and a stalagmite meet and fuse together.
  710. stalagmite
    a cylinder of calcium carbonate projecting upward from the floor of a limestone cave
    Column=A dripstone or speleothem formed when a stalactite and a stalagmite meet and fuse together.
  711. standard pressure
    a unit of pressure: the pressure that will support a column of mercury 760 mm high at sea level and 0 degrees centigrade
    The boiling point of pure water at standard pressure is 100°C or 212°F.
    Bolide=An exploding meteorite.
  712. stationary
    not capable of being moved
    Cold front=A front that forms when moving cold air collides with stationary or slower moving warm air.
  713. steep
    having a sharp inclination
    Alluvial fan=A fan-like accumulation of sediment created where a steep stream slows down rapidly as it reaches a relatively flat valley floor.
  714. stratified
    deposited or arranged in horizontal layers
    Drumlin=An elongate hill formed when a glacier flows over and reshapes a mound of till or stratified drift.
  715. stratify
    form, arrange, or deposit in layers
    Drumlin=An elongate hill formed when a glacier flows over and reshapes a mound of till or stratified drift.
  716. stratosphere
    the atmospheric layer between the troposphere and the mesosphere
    The most common layer designations are: the troposphere, the stratosphere, the mesosphere and the exosphere.
  717. stratus
    a large dark low cloud
    Altostratus cloud=A high-level stratus cloud.
  718. stream
    a natural body of running water flowing on or under the earth
    Alluvial fan=A fan-like accumulation of sediment created where a steep stream slows down rapidly as it reaches a relatively flat valley floor.
  719. streamer
    a long flag; often tapering
    A cloud-like streamer or trail often seen behind aircraft flying in clear, cold, humid air.
  720. stress
    special emphasis attached to something
    Compressive stress=Stress that acts to shorten an object by squeezing it.
  721. structure
    a thing constructed; a complex entity constructed of many parts
    Cross cutting relationship=Any relationship in which younger rocks or geological structures interrupt or cut across older rocks or structures.
  722. subdivision
    the act of subdividing; division of something previously divided
    Epoch=a subdivision of a geological period on the geologic timetable.
  723. subduction
    a geological process in which one edge of a crustal plate is forced sideways and downward into the mantle below another plate
    Active continental margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: Andean margin)
    Active volcano=A volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
  724. subsurface
    beneath the surface
    Convective zone=The subsurface zone in a star where energy is transmitted primarily by convection.
  725. sufficient
    of a quantity that can fulfill a need or requirement but without being abundant
    Disseminated ore deposit=A large low-grade ore deposit in which generally fine-grained metal-bearing minerals are widely scattered throughout a rock body in sufficient concentration to make the deposit economical to mine.
  726. sulfide
    a compound of sulphur and some other element that is more electropositive
    The black color is caused by precipitation of very fine grained metal sulfide minerals as hydrothermal solutions cool by contact with sea water.
  727. surface
    the outer boundary of an artifact or a material layer constituting or resembling such a boundary
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  728. surround
    extend on all sides of simultaneously; encircle
    Atmosphere=The envelope of gases that surround a planet's surface held by the planet's gravity.
  729. suspend
    bar temporarily; from school, office, etc.
    Aerosol=Any small particle that is larger than a molecule and suspended in air.
  730. suspended
    (of undissolved particles in a fluid) supported or kept from sinking or falling by buoyancy and without apparent attachment
    Aerosol=Any small particle that is larger than a molecule and suspended in air.
  731. technical
    of or relating to technique or proficiency in a practical skill
    Blizzard=Although blizzard is often used to describe any major snow storm with strong winds, the technical definition for a blizzard requires at least 3 hours in duration; low temperatures (usually less than minus 7C or 20F), strong winds (greater than 55 km/h or 35 mph), blowing snow which reduces visibility to less that 1 kilometer (0.6 miles).
  732. technique
    a practical method or art applied to some particular task
    Absolute dating=A technique that geologists use to assign specific dates to rock formations and geologic events.
  733. tectonic
    pertaining to the structure or movement of the earth's crust
    Basin=A low area of the Earth's crust of tectonic origin, commonly filled with sediment.
  734. tectonics
    the branch of geology studying the folding and faulting of the earth's crust
    The continental drift theory has been replaced by the more complete plate tectonics theory.
  735. temperature
    the degree of hotness or coldness of a body or environment (corresponding to its molecular activity)
    Absolute Zero=Considered to be the point at which theoretically no molecular activity exists or the temperature at which the volume of a perfect gas vanishes.
  736. temporarily
    for a limited time only; not permanently
    Evacuate= Temporarily move people away from possible danger.
  737. terminus
    a place where something ends or is complete
    End moraine=A moraine that forms at the end, or terminus of a glacier.
  738. terrain
    a piece of ground having specific characteristics or military potential
    Accreted terrain=A land mass that originated as an island arc or a microcontinent that was later added onto a continent.
  739. Tertiary
    from 63 million to 2 million years ago
    Cretaceous- Tertiary boundary=A major stratigraphic boundary on Earth marking the end of the Mesozoic Era, best known as the age of the dinosaurs.
  740. theoretically
    in theory; according to the assumed facts
    Absolute Zero=Considered to be the point at which theoretically no molecular activity exists or the temperature at which the volume of a perfect gas vanishes.
  741. theory
    a belief that can guide behavior
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  742. theory of relativity
    (physics) the theory that space and time are relative concepts rather than absolute concepts
    E=mc2 Einstein's famous theory of relativity formula known as the energy-mass relation.
  743. thermal
    relating to or associated with heat
    Blackbody temperature=The temperature of an object if it is reradiating all the thermal energy that has been added to it; if an object is not a blackbody radiator, it will not reradiate all the excess heat and the leftover will go toward increasing its temperature.
  744. thermometer
    measuring instrument for measuring temperature
    Dry=bulb thermometer=A thermometer used to measure the ambient temperature.
  745. thick
    not thin; of a specific thickness or of relatively great extent from one surface to the opposite usually in the smallest of the three solid dimensions
    Continental climate=large yearly temperature ranges
    Continental Crust=Solid, outer layers of the earth, including the rocks of the continents; thick, low density, granitic, and old.
  746. thrive
    make steady progress; be at the high point in one's career or reach a high point in historical significance or importance
    Carbonate platform=An extensive accumulation of limestone such as the Florida Keys and the Bahamas, formed on a continental shelf in warm regions where sediment does not muddy the water and reef-building organisms thrive.
  747. thunderstorm
    a storm resulting from strong rising air currents; heavy rain or hail along with thunder and lightning
    Downbursts occur in regions of a severe thunderstorm where the air is accelerated downward by exceptionally strong evaporative cooling occurs (a dry downburst) or by very heavy rain which drags dry air down with it (a wet downburst).
  748. tidal
    of or relating to or caused by tides
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  749. tidewater
    low-lying coastal land drained by tidal streams
    Calving=A process in which large chunks of ice break off from tidewater glaciers to form icebergs.
  750. tilt
    heel over
    Angular unconformity=An unconformity in which younger sediment or sedimentary rocks rest on the eroded surface of tilted orfolded older rocks.
  751. topographic
    concerned with topography
    Contour interval=the difference in elevation between two consecutive contour lines
    Contour line=line on a topographic map that connects points on land that have the same elevation.
  752. topography
    the configuration of a surface and the relations among its man-made and natural features
    The data is then used to record the topography of the sea floor.
  753. topsoil
    the layer of soil on the surface
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  754. tract
    an extended area of land
    Delta=The nearly flat, alluvial, fan-shaped tract of land at the mouth of a stream.
  755. transfer
    move from one place to another
    Convection=Fluid (gas or liquid) circulation driven by temperature and density differences; the transfer of heat by this automatic circulation (currents).
  756. transmit
    send from one person or place to another
    Convective zone=The subsurface zone in a star where energy is transmitted primarily by convection.
  757. transmitted
    occurring among members of a family usually by heredity
    Convective zone=The subsurface zone in a star where energy is transmitted primarily by convection.
  758. transparent
    transmitting light; able to be seen through with clarity
    Also refers to thin, transparent ice on road surfaces.
  759. transport
    move something or somebody around; usually over long distances
    Bed load=That portion of a stream's load that is transported on or immediately above the stream bed.
  760. trigger
    lever that activates the firing mechanism of a gun
    Branching chain reaction=A nuclear fission reaction in which the initial reaction releases two or three neutrons, each of which triggers the fission of additional nuclei.
  761. tropical
    relating to or situated in or characteristic of the tropics (the region on either side of the equator)
    Also a synonym for a tropical cyclone, or hurricane.
  762. troposphere
    the lowest atmospheric layer; from 4 to 11 miles high (depending on latitude)
    The most common layer designations are: the troposphere, the stratosphere, the mesosphere and the exosphere.
  763. tuff
    hard volcanic rock composed of compacted volcanic ash
    Ash flow=A mixture of volcanic ash, larger pyroclastic particles, and gas that flows rapidly along the Earth's surface as a result of an explosive volcanic eruption. (syn: nuee ardente)
    Ash=flow tuff-A pyroclastic rock formed when an ash flow solidifies.
  764. turbulent
    characterized by unrest or disorder or insubordination
    Ash Flow=A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure.
  765. typical
    exhibiting the qualities or characteristics that identify a group or kind or category
    Climate= typical weather patterns over a period of years in a given location
    Climate=The composite pattern of long-term weather conditions that can be expected in a given region.
  766. ultimate
    furthest or highest in degree or order; utmost or extreme
    The ultimate base level is usually sea level, but this is seldom attained.
  767. ultimately
    as the end result of a succession or process
    Drainage basin=The region that is ultimately drained by a single river.
  768. ultraviolet
    having or employing wavelengths shorter than light but longer than X-rays; lying outside the visible spectrum at its violet end
    Chert=A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
    Chlorofluorocarbons=(CFC's); gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
  769. unconsolidated
    loose and unstratified
    Alluvium=A general term for clay, silt, sand, gravel or similar unconsolidated material deposited by a stream or other body of running water.
  770. undefined
    not precisely limited, determined, or distinguished
    Asthenosphere=The shell within the earth, some tens of kilometers below the surface and of undefined thickness, which is a shell of weakness where plastic movements take place to permit pressure adjustments.
  771. underlie
    lie underneath
    Bedrock=The solid rock that underlies soil or regolith.
  772. uneven
    (of a contest or contestants) not fairly matched as opponents
    Differential weathering=The process by which certain rocks weathers more rapidly than adjacent rocks usually resulting in an uneven surface.
  773. universe
    everything that exists anywhere
    Big Bang Hypothesis=The theory that the universe was originally a single dense sphere of hydrogen that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
  774. upper mantle
    the upper part of the mantle
    Asthenosphere=The portion of the upper mantle beneath the lithosphere.
  775. valley
    a long depression in the surface of the land that usually contains a river
    Alluvial fan=A fan-like accumulation of sediment created where a steep stream slows down rapidly as it reaches a relatively flat valley floor.
  776. vapor
    a visible suspension in the air of particles of some substance
    Absolute Humidity=The ratio of the mass of water vapor present in the air to the volume occupied by the gas; the density of water vapor in the air, usually expressed as grams of water vapor per cubic meter of air.
  777. vapor pressure
    the pressure exerted by a vapor; often understood to mean saturated vapor pressure (the vapor pressure of a vapor in contact with its liquid form)
    The temperature at which the equilibrium vapor pressure between a liquid and its vapor is equal to the external pressure on the liquid.
  778. variation
    the process of varying or being varied
    Climate refers to yearly cycles of temperature, wind, rainfall, etc., and not to daily variations (see "weather").
  779. vary
    become different in some particular way, without permanently losing one's or its former characteristics or essence
    One other important constituents of air is water vapor (H2O) which varies from 0% to about 4%.
  780. varying
    marked by diversity or difference
    Extend varying distances outward from the exposed continental margins.
  781. velocity
    distance travelled per unit time
    Black hole=An object whose gravity is so strong that the escape velocity exceeds the speed of light.
  782. vent
    a hole for the escape of gas or air
    Ash=Fine particles of pulverized rock blown from an explosion vent.
  783. vernal
    suggestive of youth; vigorous and fresh
    Equinox=The date when the sun is directly overhead at noon on the equator, occurring on or around both March 21 and September 22, the former is the vernal (spring) equinox and the latter the autumnal (fall) equinox in the Northern Hemisphere and the reverse on the Southern Hemisphere.
  784. vertical
    at right angles to the plane of the horizon or a base line
    In meteorology, horizontal air flow is called advection, whereas convection is reserved for vertical air flow.
  785. vicinity
    a surrounding or nearby region
    Most of the May 18, 1980 deposits in the upper valley of the North Fork Toutle River and in the vicinity of Spirit Lake are from the debris avalanche.
  786. visibility
    quality or fact or degree of being visible; perceptible by the eye or obvious to the eye
    Often these snow storms have high winds reaching 100 km/h which reduce visibility through blowing and drifting snow.
  787. visible
    capable of being seen; or open to easy view
    Cloud=A visible collection of minute particle matter, such as water droplets and/or ice crystals, in the free air.
  788. volcanic
    igneous rock produced by eruption and solidified on or near the earth's surface; rhyolite or andesite or basalt
    Andean margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: active continental margin)
    Andesite=Intermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
  789. volcano
    a fissure in the earth's crust (or in the surface of some other planet) through which molten lava and gases erupt
    Active continental margin=A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate. (syn: Andean margin)
    Active volcano=A volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
  790. volume
    the property of something that is great in magnitude
    Absolute Humidity=The ratio of the mass of water vapor present in the air to the volume occupied by the gas; the density of water vapor in the air, usually expressed as grams of water vapor per cubic meter of air.
  791. wastage
    the process of wasting
    Ablation area=The lower portion of a glacier where more snow melts in summer than accumulates in winter so there is a net loss of glacial ice. (syn: zone of wastage)
    Abrasion=wearing away of a rock by grinding action.
  792. water level
    the level of the surface of a body of water
    Artesian Well=A well in an aquifer where the groundwater is confined under pressure and the water level will rise above the top of the confined aquifer.
  793. water table
    underground surface below which the ground is wholly saturated with water
    Cone of depression=A cone-like depression in the water table formed when water is pumped out of a well more rapidly than it can flow through the aquifer.
  794. wave
    (physics) a movement up and down or back and forth
    Alternative energy resources=All energy resources other than fossil fuels and nuclear fission; including solar energy; hydroelectric power; geothermal energy; wind energy; biomass energy; tidal, wave, and heat energy from the seas; and nuclear fusion.
  795. wavelength
    a shared orientation leading to mutual understanding
    Doppler effect=The apparent change in wavelength of sound or light caused by the motion of the source, observer or both.
  796. wax
    any of various substances of either mineral origin or plant or animal origin; they are solid at normal temperatures and insoluble in water
    Petroleum, asphalt, natural mineral wax, and asphaltites are all bitumens.
  797. weather
    the atmospheric conditions that comprise the state of the atmosphere in terms of temperature and wind and clouds and precipitation
    A horizon=The uppermost layer of soil composed of a mixture of organic matter and leached and weathered minerals. (syn: topsoil)
    Aa=Hawaiian term used to describe a lava flow whose surface is broken into rough angular fragments.
  798. Wegener
    German geophysicist who proposed the theory of continental drift (1880-1930)
    Continental drift=The theory proposed by Alfred Wegener that continents were once joined together and later split and drifted apart.
  799. wetland
    a low area where the land is saturated with water
    Clean Water Act=A federal law mandating the cleaning of the nation's rivers, lakes, and wetlands, and forbidding the discharge of pollutants into waterways.
  800. whistle
    the sound made by something moving rapidly or by steam coming out of a small aperture
    Named for J. Christian Doppler, an Austrian physicist, who in 1842 explained why the whistle of an approaching train had a higher pitch than the same whistle when the train was going away.
  801. white dwarf
    a faint star of enormous density
    Degeneracy pressure=The strength of the atomic particles that holds a white dwarf star from further collapse.
  802. wind
    air moving (sometimes with considerable force) from an area of high pressure to an area of low pressure
    The surface movement that is commonly called wind.
  803. wispy
    thin and weak
    Cirrus cloud=A wispy, high-level cloud.
  804. withstand
    resist or confront with resistance
    Elastic limit=The maximum stress that an object can withstand without permanent deformation.
  805. zero
    a mathematical element that when added to another number yields the same number
    Absolute Zero=Considered to be the point at which theoretically no molecular activity exists or the temperature at which the volume of a perfect gas vanishes.