Evolution of the atmosphere

• How long ago did the earth form

  4.6 billion years ago
• What is the composition of our current atmosphere

  78% nitrogen

  21% oxygen

  1% argon

  0.04% carbon dioxide
• 3 main stages in the evolution of Earths atmosphere

  Phase 1 - volcanoes emitted large amounts of gas

  Phase 2 - Earth cooled, oceans formed, plants and algae evolved

  Phase 3 - plants and algae produced oxygen, eventually forming the atmosphere we have today
• What happened to earths atmosphere in the first billion years

  The surface was very volcanic releasing lots of carbon dioxide and nitrogen, alongside smaller amounts of water vapour, ammonia, and methane
• How were oceans formed

  After 1 billion years the Earth cooled causing water vapour in the atmosphere to condense into liquid and form oceans
• What happened to most of the carbon dioxide in the early atmosphere

  Dissolved in oceans

  Dissolved CO2 then went through a series of reactions to form carbonate precipitates

  These carbonate precipitates formed sediments on the sea bed

  Some CO2 was also absorbed by green plants and algae so they could photosynthesise
• What is limestone made from

  Made from calcium carbonate deposits from the shells and skeletons of marine organisms
• When did algae start producing oxygen

  2.7 billion years ago
• Why is evidence for the earths early atmosphere limited

  It was a very long time ago so there is little evidence remaining
• How are coal, crude oil and natural gas formed

  Plants or algae absorb CO2 to use in photosynthesis

  When they die they don’t decompose properly

  Under high temperatures and pressures the organic mater forms coal, crude oil or natural gas
• How has the atmosphere changed since the Earth was formed


  Volcanos released larger amounts of nitrogen and carbon dioxide

  As the Earth cooled the water vapour condensed to form the oceans

  Carbon dioxide dissolved in oceans to form carbonates

  Carbonates produced sediments which formed sedimentary rock

  Algae and plants appeared and absorbed carbon dioxide by photosynthesis

  Carbon was locked up in fossil fuels