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