GEOLOGIC TIME SCALE

Organizing Geologic TimeGeologic Time Scale - series of time intervals that record Earth’s history from its origin 4.6 billion years ago (bya) to present

Intervals are divided using significant events and fossils

Enables scientists to find relationships among geological events, environmental conditions, and fossilized life forms

EonEon - largest interval of geologic time - half a billion years or more

4 Eons - Hadean, Archean, Proterozoic, and Phanerozoic

First 3 eons make up ~90% of geologic time - known together as the Precambrian

Eons are made up of eras

EraEra - tens to hundreds of millions of years in duration

Defined by different life forms found in rocks

Named based on relative ages of life forms

Paleo - old, meso - middle, ceno - recent

3 Eras - Paleozoic, Mesozoic, Cenozoic

Eras are divided into periods

PeriodPeriod - tens of millions of years in duration

Named for geographic region where rocks/fossils were first observed and described

Periods are divided into epochs

Paleozoic and Mesozoic Periods

EpochEpoch - hundreds of thousands to millions of years in duration

All periods of time are divide into epochs - not all shown on scale

Currently We Are In...

Eon - Phanerozoic

Era - Cenozoic

Period - Quaternary

Epoch - Holocene

Geologic Time Scale