composition and evolution of atmosphere

• describe the proportion of gasses in the atmosphere

  • 80% nitrogen
  • 20% oxygen
  • small proportions of other gasses eg co2 water vapour and noble gasses
• why is evidence about early atmosphere limited

  huge time scale of 4.6 billion years
• how did volcanoes affect early atmosphere

  for the first billion years released gasses like methane nitrogen ammonia carbon dioxide and water vapour
• what happened to water vapour in the early atmosphere

  condensed to form oceans
• earths early atmosphere was like which other planets

  mars and venus - lots of co2 and little to no oxygen gas
• where did the high proportion if nitrogen come from

  volcanoes
• what effect did the ocean have on co2

  • co2 dissolved in the water and carbonates were precipitated producing sediments eg limestone
• how did oxygen increase and when

  • algae and plants produced oxygen in photosynthesis
  • started producing about 2.7 billion years ago
  • over next billion more plants evolved and oxygen increased to a level where animals could evolve
• how did co2 decrease

  • algae and plants decreased co2 in photosynthesis
  • formation of sedimentary rocks eg limestone
  • formation of fossil fuels that contain carbon eg coal, crude oil, natural gas
• photosynthesis equation

  carbon dioxide + water - oxygen + glucose

  6Co2 + 6H2O - 6O2 + C6H12O6