Across
- 4. eras are divided into these
- 5. the longest period of time on Earth
- 6. Humans evolve
- 10. first amphibians
- 11. first birds
- 13. mostly invertebrates
- 14. great coal deposits form
Down
- 1. first dinosaurs
- 2. the number of eras in the history of earth
- 3. first placental mammals
- 5. first reptiles
- 7. first vertebrates
- 8. flowering plants are dominant
- 9. first jawed fish
- 12. humans evolved ___ million years ago