Evolution of the Atmosphere

• The earth's atmosphere is composed of about 80% nitrogen, 20% oxygen, and less than 1% of other gases like carbon dioxide, water vapor, and noble gases
• How the earth's atmosphere evolved

  1. Volcanic activity produced CO2, water vapor, nitrogen, methane, ammonia

  2. Water vapor condensed into oceans, allowing CO2 to dissolve

  3. Algae and plants evolved, using CO2 for photosynthesis and producing O2

  4. Organic matter from dead algae/plants became buried and formed fossil fuels
• The early atmosphere was mostly CO2, similar to Mars and Venus today
• As algae and plants evolved and photosynthesized, atmospheric CO2 levels declined and O2 levels increased
• More complex life like animals could evolve due to the increased O2 levels
• Types of sedimentary rocks/fossil fuels formed from buried organic matter

  • Crude oil
  • Natural gas
  • Coal
  • Limestone
• Crude oil and natural gas are formed mainly from dead plankton
• Coal is formed from thick deposits of dead plant material
• Limestone is formed mostly from the calcium carbonate in marine organism shells and skeletons
• This process of atmosphere evolution is a theory, although supported by evidence