Phanerozoic

The Phanerozoic (British English Phanærozoic) is the current geologic eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years (541.0 ± 1.0) and goes back to the time when diverse hard-shelled animals first appeared. Its name derives from the Ancient Greek words φανερός and ζωή, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon. The time before the Phanerozoic, called the Precambrian supereon, is now divided into the Hadean, Archaean and Proterozoic eons.