The Earth's atmosphere

• How old is the Earth?

  4.6 billion years
• For how many years have the proportions of different gases been the same in the atmosphere?

  200 million years
• What are the proportions of the gases in the Earth's atmosphere?

  80 % nitrogen, 20 % oxygen and small proportions of various other gases including carbon dioxide water vapour and noble gases
• What happened during the first billion years of the Earth's existence?

  there was intense volcanic activity that released the gases that formed the early atmosphere and water vapour that cooled and condensed to form the oceans.
• What was the early atmosphere like?

  atmosphere of Venus or Mars today
• What were the main gases in the early atmosphere?

  Carbon dioxide, Methane, Ammonia, Water vapour
• What did volcanoes produce in the early atmosphere?

  nitrogen which gradually built up in the atmosphere
• What happened when oceans started to form?

  When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments , reducing the amount of carbon dioxide in the atmosphere
• How oxygen increased


  Algae and plants produced the oxygen by photosynthesis
• What is the photosynthesis equation?

  Carbon dioxide + water → glucose + oxygen
• How carbon dioxide decreased

  -Plants photosynthesising

  -Locked up in sedimentary rocks

  -Locked up in fossil fuels

  -Absorbed in the oceans

  -The sedimentary rock , limestone which is mainly calcium carbonate , formed the shells and skeletons of marine organisms