Atmosphere

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Across
  1. 3. Produced with carbon dioxide when fuels are combusted
  2. 4. The Earth is ____.6 billion years old
  3. 5. What is the main gas in todays atmosphere?
  4. 8. This greenhouse gas is made from farming cattle
  5. 10. Where did all the Carbon Dioxide come from?
Down
  1. 1. A greenhouse gas
  2. 2. What was the main gas in the earth's early atmosphere?
  3. 6. What gas makes up 20% of the atmosphere?
  4. 7. From what was oxygen first produced?
  5. 9. Algae first evolved _____.7 billion years ago