| A | B |
|---|
| Epoch | shortest division in geologic time |
| Eon | longest division in geologic time |
| Evolution | gradual change in life-forms over time |
| Natural selection | organisms with best traits for environment survive |
| Mass extinction | large numbers of species die out completely |
| Precambrian Era | includes 88% of geologic time |
| Mesozoic Era | called Age of Reptiles |
| Casts | molds filled with sediment |
