geological time

Definitions of geological time

n the time of the physical formation and development of the earth (especially prior to human history)

geologic time
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Phanerozoic aeon
the period from about 5,400 million years ago until the present
Age of Mammals
approximately the last 63 million years
Quaternary period
last 2 million years
Holocene epoch
approximately the last 10,000 years
Pleistocene epoch
from two million to 11 thousand years ago; extensive glaciation of the northern hemisphere; the time of human evolution
Tertiary period
from 63 million to 2 million years ago
Pliocene epoch
from 13 million to 2 million years ago; growth of mountains; cooling of climate; more and larger mammals
Miocene epoch
from 25 million to 13 million years ago; appearance of grazing mammals
Oligocene epoch
from 40 million to 25 million years ago; appearance of sabertoothed cats
Eocene epoch
from 58 million to 40 million years ago; presence of modern mammals
Paleocene epoch
from 63 million to 58 million years ago; appearance of birds and earliest mammals
Age of Reptiles
from 230 million to 63 million years ago
Cretaceous period
from 135 million to 63 million years ago; end of the age of reptiles; appearance of modern insects and flowering plants
Jurassic period
from 190 million to 135 million years ago; dinosaurs; conifers
Triassic period
from 230 million to 190 million years ago; dinosaurs, marine reptiles; volcanic activity
Paleozoic era
from 544 million to about 230 million years ago
Permian period
from 280 million to 230 million years ago; reptiles
Carboniferous period
from 345 million to 280 million years ago
Upper Carboniferous period
from 310 million to 280 million years ago; warm climate; swampy land
Lower Carboniferous period
from 345 million to 310 million years ago; increase of land areas; primitive ammonites; winged insects
Devonian period
from 405 million to 345 million years ago; preponderance of fishes and appearance of amphibians and ammonites
Silurian period
from 425 million to 405 million years ago; first air-breathing animals
Ordovician period
from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds
Cambrian period
from 544 million to about 500 million years ago; marine invertebrates
Precambrian period
the eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago
Proterozoic aeon
from 2,500 to 544 million years ago; bacteria and fungi; primitive multicellular organisms
Archaeozoic aeon
the time from 3,800 million years to 2,500 million years ago; earth's crust formed; unicellular organisms are earliest forms of life
Priscoan aeon
the earliest eon in the history of the Earth from the first accretion of planetary material (around 4,600 million years ago) until the date of the oldest known rocks (about 3,800 million years ago); no evidence of life
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aeon, eon
the longest division of geological time
geological period, period
a unit of geological time during which a system of rocks formed
era, geological era
a major division of geological time; an era is usually divided into two or more periods
a unit of geological time that is a subdivision of a period and is itself divided into ages
glacial epoch, glacial period, ice age
any period of time during which glaciers covered a large part of the earth's surface
Type of:
the continuum of experience in which events pass from the future through the present to the past

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