Across
- 2. improves adaptation
- 4. source of atmosphere
- 5. star orbiter
- 6. photosynthesis product
- 7. cooperating life-forms
- 9. supercontinent
- 13. eon of visible life
- 14. woolly elephant
- 16. crater maker
- 17. earliest life-forms
- 18. terrible lizard
Down
- 1. gas layer around earth
- 3. eating sunlight
- 6. where life originated
- 8. second eon (no oxygen)
- 9. third eon (has oxygen)
- 10. human specie (2 words)
- 11. disk around early sun
- 12. underwater volcano
- 15. eon of hellish earth