Atmosphere

• What is the approximate percentage of nitrogen in the atmosphere?

  78%
• What is the approximate percentage of oxygen in the atmosphere?

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

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

  For around 200 million years
• How old is the Earth?

  Approximately 4,600 million years
• What was the state of the Earth's atmosphere during the first billion years?

  It consisted mainly of carbon dioxide with little or no oxygen
• What gases did volcanoes release that contributed to the early atmosphere?

  Water vapor, carbon dioxide, nitrogen, methane, and ammonia
• How did the early atmosphere compare to the atmospheres of Mars and Venus today?

  It was very much like the atmospheres of Mars and Venus today
• What happened to the carbon dioxide as the Earth cooled?

  It dissolved in the oceans and formed weak acids
• What did the weak acid formed from dissolved carbon dioxide react with?

  Minerals in the sea to form precipitates
• What did the sediments formed from the weak acid eventually become?

  Carbonate rock on the seabed
• How did corals and shells contribute to the reduction of carbon dioxide in the atmosphere?

  They used carbon dioxide to form limestone when they died
• What significant event occurred around 2.7 billion years ago?

  Photosynthetic algae first evolved in the oceans
• What process produced oxygen that entered the atmosphere?

  Photosynthesis
• What was the effect of the evolution of plants on the atmosphere?

  It increased the amount of oxygen in the atmosphere
• What is the relationship between photosynthesis and carbon dioxide levels in the atmosphere?

  Photosynthesis takes in carbon dioxide, reducing its levels
• What are the main changes in the atmosphere from the early Earth to now?

  • Early atmosphere: High carbon dioxide, low oxygen
  • Current atmosphere: Low carbon dioxide, 21% oxygen
  • Nitrogen levels increased over time
• How do fossil fuels relate to carbon dioxide levels in the atmosphere?

  • Carbon can be trapped in fossil fuels
  • This process reduces carbon dioxide levels in the atmosphere