| A | B |
|---|
| eon | largest division of geologic time |
| era | what eons are divided into |
| evolution | gradual change in a life form over time |
| natural selection | survival of the fittest |
| mass extinction | enormous number of species disappear |
| epoch | shortest division of geologic time |
| periods | what eras are divided into |
| stromatolite | algae mats in shallow water |
