1
Precambrian
makes up about 88% to 90% of Earth’s history
2
Cambrian
Age of Trilobites
3
Devonian
Age of Fishes (Paleozoic era)
4
Cenozoic
Age of Mammals
5
Paleozoic
first reptiles and insects appeared
6
Superposition
A law of rock layers that states the lowest rock layer is the oldest
7
Unconformity
A layer of rock that separates two or more other layers of rock
8
index fossil
A fossil that has not lived for a long time and appeared a lot