eon

5 ENTRIES FOUND:

eon

Long span of geologic time. In formal usage, eons are the longest portions of geologic time (eras are the second-longest). Three eons are recognized: the Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), the Proterozoic Eon, and the Archean Eon. Less formally, eon often refers to a span of one billion years.

This entry comes from Encyclopædia Britannica Concise.
For the full entry on eon, visit Britannica.com.

Seen & Heard

What made you look up eon? Please tell us what you were reading, watching or discussing that led you here.