gases today

• GASES IN ATMOSPHERE TODAY: stayed constant for around 200 million years

  nitrogen = 80%

  oxygen = 20%

  small proportions of other gases, i.e.:

  • carbon dioxide
  • water vapour
  • noble gases
• scientists cannot be certain about the early atmosphere since evidence is limited because of the time scale of 4.6 billion years
• theory: volcanoes

  during the first billion years, there was intense volcanic activity, releasing gases that formed in the atmosphere:

  • water vapour
  • carbon dioxide
  • nitrogen
• in the early atmosphere, the volcanic activity released water vapour and as the earth cooled, it condensed to form oceans
• in the early atmosphere, the volcanic activity released, carbon dioxide, so the earth's atmosphere consisted mainly of carbon dioxide with little to no oxygen (so like Mars and Venus today)
• in the early atmosphere, the volcanic activity released nitrogen, which gradually built up in the atmosphere, and there may of been small amounts of methane and ammonia
• so, the earths early atmosphere consisted of mainly carbon dioxide, with small but increasing amounts of nitrogen
• differences between early and today:

  • early contained large amounts of carbon dioxide, today only contains small amounts
  • early contained very little oxygen, but today is it 20%
• when the oceans formed, some of the carbon dioxide dissolved in the water = weak acid so:

  carbonates were precipitated producing sediments (carbonate rock)

  also made corals and shells of organisms such as mussels ; died = limestone

  which reduces the amount of carbon dioxide in the atmosphere
• Carbon dioxide decreased through plants and algae photosynthesising
• oxygen increase:

  2.7 billion years ago, algae first produced oxygen through photosynthesis which entered the atmosphere

  over the next billion years, plants evolved, increasing oxygen to a level that enabled animals to evolve
• photosynthesis equation:

  carbon dioxide + water --> glucose + oxygen

  6CO2 + 6H2O --> C6H12O6 + 6O2
• photosynthesis releases oxygen but also takes in carbon dioxide

  the carbon can be trapped in fossil fuels (containing carbon) and was also reduced due to the formation of sedimentary rocks

  decreasing level of carbon dioxide
• gases in atmosphere has stayed constant for around 200 million years