The Atmosphere

• What is the main gas in the atmosphere today?

  Nitrogen
• What percentage of the atmosphere is nitrogen?

  78%
• 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
• How old is the Earth?

  4,600 million years
• What was the composition of the early atmosphere?

  Mainly carbon dioxide with little oxygen
• What gases did volcanoes release during the early atmosphere?

  Water vapor, carbon dioxide, nitrogen
• What happened to water vapor as the Earth cooled?

  It condensed to form oceans
• What did carbon dioxide dissolve in the oceans to form?

  A weak acid
• What did the weak acid react with in the sea?

  Minerals
• What did the reaction of carbon dioxide and minerals form?

  Precipitates and sediments of carbonate rock
• How did corals and shells contribute to the carbon dioxide levels?

  They used carbon dioxide to form limestone
• What significant change occurred to carbon dioxide levels over time?

  They began to fall
• When did photosynthetic algae first evolve?

  Around 2.7 billion years ago
• What process produced oxygen in the atmosphere?

  Photosynthesis
• What did photosynthesis take in besides producing oxygen?

  Carbon dioxide
• What happened to carbon during photosynthesis?

  It can be trapped in fossil fuels
• What are the key differences between the early atmosphere and today's atmosphere?

  • Early atmosphere had large amounts of carbon dioxide
  • Today's atmosphere has only a small amount of carbon dioxide
  • Early atmosphere had very little oxygen
  • Today's atmosphere contains 21% oxygen
• What will be covered in the next video?

  How fossil fuels are formed
• Where can students find questions on the atmosphere?

  In the vision workbook
• How did the evolution of plants affect the atmosphere?

  It increased the amount of oxygen