| Answer | Crossword Clue |
|---|---|
| AEON | One spelling of a billion years |
| EON | Division of about one billion years |
| AEON | One billion years |
| EON | One billion years |
| AEON | One billion years (var.) |
| AEON | One billion years (Var.) |
| EONS | One billion years, geologically |
| EON | One billion years, geologically |
| EON | One billion years, in astronomy |
| EON | One billion years to Hubble |
| EON | One billion years, in geology |
| EON | One billion years in ONE? |
| EON | One billion years, to an astronomer |
| EON | One billion years, in geologic time |
| EON | The Hadean was the first one, ending about 4 billion years ago |
