| A | B |
|---|
| evolution | ancient organisms descending down |
| fitness | physical traits that help us survive |
| common descent | descending from common ancestors |
| adaptation | process that fitness arises |
| fossil | preserved remains |
| eras | divisions of 4.5 billion years of earth |
| period | divisions of eras |
| epoch | divisions of periods |
| fossil record | collection of millions of fossils |
| embryo | early stages of development |
