GEOLOGICAL TIME

The Earth is about 4.5 billions years old. During its long life its surface has seen much transformation as a result of tectonic action, vulcanism, glaciation, asteroid impacts, changes in solar activity and life.
How Geologic time is measured

Eons
- The largest arbitrary periods of time are called Eons and account for up to billions of years.
Archeon - 4.6 to 2.5 BYA (billion years ago)
Proterozoic - 2.5 to .59 BYA
Phanerozoic - .59 BYA to the present
         Eons   have  Eras
         Eras     have  Periods
       Periods have  Epochs