Across
- 3. first living organism made of a single cell
- 4. layer, protects Earth from harmful radiation from the sun
- 8. earliest animals that developed from bacteria
- 9. plant parts that absorb water from the ground
- 10. place where the first life originated
- 11. process where organisms use energy from the sun
- 13. soft material that some fish skeletons are made of
- 14. organisms made of more than one cell
- 16. first vertebrates that lived on land
Down
- 1. extinct group of animals that once dominated Earth
- 2. animals that feed their young with milk
- 5. animals with hard-shelled eggs that survive without water
- 6. first animals that moved onto land
- 7. a living being
- 12. animals with a backbone like fish
- 15. place where plants and later animals spread to