Chemistry of the atmosphere - early

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  • the atmosphere
    • Theories suggest volcanoes release Carbon Dioxide, Water vapour and nitrogen, and that these gases formed the early atmopsphere
      • Water vapour in the atmosphere condensed the Earth gradually cooling down, and fell as rain
      • Water collected in hollows in the crust as the rock solidified and the first oceans were formed
    • Comets could've brought water to the earth
      • Icy comets rained down on the surface of the earth, as they melted, adding to its water supplies
    • As the earth began to stabilise, the atmosphere mainly consisted carbon dioxide
      • Some Nitrogen gas, water vapour, traces of methane and ammonia, but little to no oxygen
        • Resembles the atmosphere that are known today on planets like Mars and Jupiter
    • Scientists think life began around 3.4 billion years ago when the first simple organisms, like bacteria, appeared (used breakdown of chemicals as a source of energy)
      • Other simple organisms like bacteria and algae began to form, algae could use energy from the sun to make their own food
        • Level of oxygen rose steadily as algae & bacteria thrived in the seas, more plants evolved, all removing carbon dioxide and making oxygen
          • successfully colonised the earth, atmosphere richer in oxygen, possible for first animals to evolve, they relied on algae for food and oxygen to respire
    • Photosynthesis occurs and the carbon in the glucose can then end up in a new plant material
      • Carbon is transferred to animals when the eat plants, including their skeletons and shells
        • These built up at the bottom of vast oceans, they became covered with layers of fine sediment eventually deposits formed sedimentary carbonate rocks (limestone), containing calcium carbonate CaCO3
          • Some ancient remains were crushed by large scale movements of the earth, heated within crust over long periods of time, forming crude and fossil fuels
    • Evolving atmosphere
      • Coal is classed as sedimentary rock, formed from thick deposits of plant material, ancient tress & ferns
        • When plants died in swamps, they were buried in absence of oxygen, compressed over millions of years
      • Crude oil & natural gas formed from remains of plankton deposited in muds on the seabed. Covered by layers of sediment, compressed and becoming trapped beneath rock
      • Carbon dioxide gas was removed by dissolving in water in the oceans
        • Metal oxides made insoluble carbonate compounds which fell to the seabed & helped to form more carbonates
          • Natural cycle means carbon dioxide never runs out
      • Any methane and amonia found in the earths early atmosphere reacted with oxygen,  this removed them from the atmosphere
        • Nitrogen could build up as its an unreactive gas
    • early atmosphere


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