geological time period

[springersue]

period of time longer than an era

[bernardo]

aeon

[Wraith]

An epoch.

[Clanad]

The history of the Earth is broken up into a hierarchical set of divisions for describing geologic time. As increasingly smaller units of time, the generally accepted divisions are Eon, Era, Period, Epoch, and Age. So bernardo is entirely correct (taking into consideration European spelling)... at least insofar as I was was instructed studying geology eons ago...