The Atmosphere

• What is the main gas in the atmosphere today?

  Nitrogen
• What percentage of the atmosphere is oxygen?

  21%
• What are the other gases present in the atmosphere besides nitrogen and oxygen?

  Carbon dioxide, water vapor, noble gases
• How long have the gases in the atmosphere remained constant?

  Around 200 million years
• What was the Earth's atmosphere mainly composed of during the first billion years?

  Mainly carbon dioxide
• What caused the early atmosphere to change?

  Intense volcanic activity
• What gas was released by volcanoes that contributed to the early atmosphere?

  Water vapor
• What happened to water vapor as the Earth cooled?

  It condensed to form oceans
• What gases did volcanoes release besides carbon dioxide?

  Nitrogen, methane, ammonia
• How did the level of carbon dioxide change over time?

  It began to fall
• What process removed carbon dioxide from the atmosphere?

  Formation of carbonate rocks
• What evolved around 2.7 billion years ago that produced oxygen?

  Photosynthetic algae
• What is the equation of photosynthesis?

  6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• What happens to carbon during photosynthesis?

  It can be trapped in fossil fuels
• What are the key changes in the atmosphere from early times to now?

  • Early atmosphere: high carbon dioxide, low oxygen
  • Current atmosphere: low carbon dioxide, 21% oxygen
  • Formation of oceans and carbonate rocks
  • Evolution of photosynthetic organisms increased oxygen
• What is the significance of the evolution of plants in the atmosphere's history?

  Increased the amount of oxygen
• Where can students find questions on the atmosphere?

  In the vision workbook
• How did the formation of limestone affect atmospheric carbon dioxide levels?

  It removed carbon dioxide from the atmosphere
• What role did oceans play in the early atmosphere's evolution?

  They dissolved carbon dioxide and formed sediments