24 Biggest Episodes of Earth

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Across
  1. 1. birds developed from feathered what (19)
  2. 5. what eukaryote cells absorbed what to obtain a new energy source (6)
  3. 7. force that pulls matter together (1)
  4. 10. Earth is 4.5 what years old (title slide)
  5. 11. this process began about 3 billion years (4) two words
  6. 13. first appeared on Earth about 130 MYA (20)
  7. 14. this process made considerable gains about 30 MYA (23)
  8. 17. relatives of this were probably the first plants to live on land (11) two words
Down
  1. 2. the end result of photosynthesis (3)
  2. 3. these seemed to evolve multiple cells before animals (8)
  3. 4. complex life form formed after the Earth froze about 200 MYA (9)
  4. 6. about 1.2 billion years ago organisms started sharing this (7)
  5. 8. life may of started near warm alkaline what (2)
  6. 9. first mammals were small and what like (17)
  7. 11. name of supercontinent that broke apart about 175 MYA (15)
  8. 12. period where the first mass extinction occurred (12)
  9. 15. the earth’s atmosphere was void of this gas until about 2.4 billion years ago (5)
  10. 16. era where the first reptiles started to appear (14)