Earth's History

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Across
  1. 2. Formed when plants and fungus broke down rocks.
  2. 5. Mass extinctions often marked the end of one ___ and the beginning of another.
  3. 6. Energy from the ___ split water molecules and put oxygen into our atmosphere.
  4. 9. The first three Eons.
  5. 11. The first form of life on Earth.
  6. 13. Eon when there was no oxygen in the atmosphere.
  7. 14. Plants and animals we know have existed on Earth for a ___ time.
  8. 16. When a large percentage of species disappears from the Earth.
  9. 17. The Eon life first appeared.
  10. 18. Compared to the age of the Earth, the Himalayan, Alps, Andes and Rocky Mountains are ___.
Down
  1. 1. The largest mass extinction.
  2. 2. Which came first, single or multi celled organisms?
  3. 3. Where on Earth life first lived.
  4. 4. When most major animal groups suddenly developed on Earth.
  5. 7. The Eon we live in.
  6. 8. ___ went extinct during the K-T extinction.
  7. 10. Which came first, oceans or rain?
  8. 12. The Era we live in.
  9. 15. Our atmosphere currently has about 20% ___.