The Atmosphere

• atmosphere = mixture of gases that surround the Earth
• original atmosphere was formed by gases given out by volcanoes
• main gases in original atmosphere:

  • carbon dioxide
  • water vapour
  • Ammonia (a small amount)
• as Earth cooled down , water vapour in atmosphere condensed ( gas -> liquid ) to form the oceans -> happened quickly in geographical terms
• carbon dioxide in atmosphere decreased due to development of photosynthesising plants -> took billions of years
• oxygen first appeared due to photosynthesis
• oxygen gas + ammonia gas reacted together to produce nitrogen gas -> took billions of years
• todays atmosphere=

  • Nitrogen
  • Oxygen
  • Argon
  • Carbon dioxide
  • other gases (including neon)
• other reasons for decrease in carbon dioxide:

  • some dissolved into oceans and seas
  • some became locked into carbonate rocks
  • some became locked into fossil fuels
• air is a source of nitrogen , oxygen , argon and neon -> can be separated because they have different boiling points