Earth's History Timeline Summary

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