| A | B |
|---|
| Geologic Time Scale | Division of Earth's history into time units based largely on the types of life forms |
| Eon | Longest subdivision in the geologic time scale |
| Era | Second longest division of geologic time |
| Period | Third longest division of geologic time |
| Epoch | Next smaller division of geologic time after the period |
| Organic evolution | Change of organisms over a geologic time |
| Species | Group of organisms that reproduces only with other members of their own group |
| Natural Selection | Suitable organisms survive in a particular environment |
| Trilobite | Index fossil with three-lobed exoskeleton in Paleozoic oceans |
| Pangaea | Large ancient landmass that was composed of all the continents |
| Precambrian Time | Longest part of Earth's history, starting at 4.0 billion years |
| Cyanobacteria | Photosynthetic bacteria thought to be one of Earth's earliest life-forms |
| Paleozoic Era | When organisms developed hard parts and ended with mass extinctions |
| Mesozoic Era | Middle era of Earth's history which Pangaea broke apart |
| Cenozoic Era | Era of recent life that began about 66 million years ago and continues today |
