| Answer | Crossword Clue |
|---|---|
| EON | Period in the earth's history |
| EON | Phanerozoic ... (current period in the earth's history) |
| PERMIAN | Period marked by the largest mass extinction in earth's history |
| NEOCENE | Period in Earth's history |
| QUATERNARY | Pertaining to the present period in earth history |
| SILVERAGE | Second-greatest period in the history of something |
