C. ORIGIN & EVOLUTIONof Earth’s Atmosphere

• General History of the Atmosphere

  • 4.5 billion yr ago - Solar System formed Early Atmosphere
  • 3 billion yr ago - Primitive life forms
  • 2 billion yr ago - First oxygen
  • 1 billion yr ago - Increased oxygen
  • 400 million yr ago - First terrestrial plants
  • 200 million yr ago - High oxygen levels

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