The Phanerozoic eon is the current eon on the geologic timescale. It is the one in which abundant animal life has existed. It covers about 541 million years, and goes back to the time when hard-shelled animals first appeared. It was once thought that life began in the Cambrian, the first period of this eon.

The time before the Phanerozoic, formerly called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.