Precambrian

makes up about 88% to 90% of Earth’s history

Cambrian

Age of Trilobites

Devonian

Age of Fishes (Paleozoic era)

Cenozoic

Age of Mammals

Paleozoic

first reptiles and insects appeared

Superposition

A law of rock layers that states the lowest rock layer is the oldest

Unconformity

A layer of rock that separates two or more other layers of rock

index fossil

A fossil that has not lived for a long time and appeared a lot