Geologic Time

Front

Record of rock layers over geologic time.

Back

Geological Column

Front

Age of rock compared to other rocks.

Back

Relative Age

Front

Age of rock in years since formation.

Back

Absolute Age

Front

In sedimentary rock, each layer is older than the one above.

Back

Law of Superposition

Front

Preserved remains or traces of past organisms.

Back

Fossil

Front

Gap in geologic record due to erosion.

Back

Unconformity

Front

Long units of geologic time.

Back

Era

Front

Units of geologic time within eras.

Back

Period

Front

Many types of living things extinct simultaneously.

Back

Mass Extinction

Front

Change in species characteristics over generations.

Back

Evolution