The Phanerozoic is the current geological eon, which started around 541 million years ago. The beginning of the Phanerozoic marks the point when abundant fossils of complex organisms suddenly appear.
The term Phanerozoic was coined in 1930 by geologist George Halcott Chadwick, from the Greek phaneros, "visible," and zoe, "life." According to the fossil record, many major animal groups first appeared at the beginning of the Phanerozoic, ones with hard parts like shells and skeletons. This is sometimes referred to as the "Cambrian Explosion." Since then, plants, fish, arthropods, and mammals have evolved. The Phanerozoic is divided into the Paleozoic, Mesozoic, and Cenozoic eras.