The Evolution of the Atmosphere

• What gas built up over time in the atmosphere?

  Nitrogen
• What did the early atmosphere probably contain mainly?

  Mainly carbon dioxide
• What were probably released in tremendous amounts over time?

  Volcanic gases
• Why is it hard to gather evidence about the early atmosphere?

  Because it was 4.6 billion years ago
• How was the early atmosphere likely similar to today?

  Like the plume of gases and steam
• What happens to water vapor upon cooling?

  It condenses
• What absorbs CO₂ from the atmosphere?

  The hydrosphere
• What has carbon ended up in over millions of years?

  Rocks and fossil fuels
• What caused an overall decrease in atmospheric CO₂?

  Processes involving absorption and sedimentation
• What do shells and skeletons contain from oceans?

  Carbonates
• What are limestone and coal classified as?

  Sedimentary rocks
• What type of deposits form crude oil and natural gas?

  Plankton deposits
• What type of deposits form from thick plant material?

  Coal deposits
• What do calcium carbonate deposits come from?

  Shells and marine skeletons
• What increased due to the arrival of algae?

  Oxygen levels in the atmosphere
• When did algae arrive?

  ~2.7 billion years ago
• What do plants produce through photosynthesis?

  Oxygen
• What is the photosynthesis equation?

  6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• What led to the evolution of animals?

  The increase in atmospheric oxygen
• What is the composition of the atmosphere today?

  ~80% N₂, ~20% O₂, noble gases, CO₂
• What are the main components of the atmosphere for the last 200 million years?

  • ~80% Nitrogen (N₂)
  • ~20% Oxygen (O₂)
  • Noble gases
  • Carbon dioxide (CO₂)