Earth's History

4. ___ went extinct during the K-T extinction.
6. The first form of life on Earth.
8. Plants and animals we know have existed on Earth for a ___ time.
11. The first three Eons.
12. The Eon life first appeared.
13. Which came first, oceans or rain?
14. Which came first, single or multi celled organisms?
15. The largest mass extinction.
17. Compared to the age of the Earth, the Himalayan, Alps, Andes and Rocky Mountains are ___.
18. The Era we live in.

1. Where on Earth life first lived.
2. Formed when plants and fungus broke down rocks.
3. When most major animal groups suddenly developed on Earth.
5. Mass extinctions often marked the end of one ___ and the beginning of another.
7. When a large percentage of species disappears from the Earth.
9. Eon when there was no oxygen in the atmosphere.
10. Our atmosphere currently has about 20% ___.
11. The Eon we live in.
16. Energy from the ___ split water molecules and put oxygen into our atmosphere.