| Answer | Crossword Clue |
|---|---|
| EON | About a billion years |
| EON | Division of about one billion years |
| EON | The Hadean was the first one, ending about 4 billion years ago |
| AEON | A billion years |
| EON | A billion years |
| EONS | A billion years, geologically |
| AEON | A billion years (Var.) |
| AEON | A billion years (var.) |
| AEON | Billion years, to a geologist |
| EON | A billion years, in geology |
| EON | A billion years, to Hubble |
| EON | A billion years, in astronomy |
| EON | A billion years, to geologists |
| AEON | A billion years, in astronomy (Var.) |
| AEON | One spelling of a billion years |
| SOLAR | Renewable energy option, for a few billion more years anyway |
