Evolution of the atmosphere

  • Phase 1 - Volcanoes gave out gases
    > the earth's surface was originally molten for many millions of years.
    > then cooled down and a thin crust formed, volcanoes kept erupting
    > volcanoes gave out lots of gases - carbon dioxide, water vapour and small amounts of other gases
    > this was how oceans and the atmosphere were formed
    > the early atmosphere was mostly CO2, virually no oxygen
    > oceans were formed when the water vapour condensed
  • Phase 2 - Green plants evolved and produced oxygen
    > a lot of the early carbon dioxide dissolved into the oceans
    > marine organisms developed, which took in some CO2, when they died the organisms were buried under layers of sediment and the CO2 became 'locked up' in carbonate rocks
    > green plants eveolved over most of the Earth
    > the green plants removed CO2 from the air and produced O2 by photosynthesis, this caused the oxygen level to gradually increase
  • Phase 3 - Ozone layer allows evolution of complex animals
    > the build up of oxygen in the atmosphere killed off some early organisms that couldn't tolerate it, but allower other more complex organisms to evolve and flourish
    > the oxygen also created the ozone layer (O3) which blocked harmful rays from the Sun and enbaled even more complex organisms to evolve - us, eventually
    > there is very little CO2 left now
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Today's Atmosphere

The Atmosphere is Still Changing
Human activity is chaning the atmosphere:

  • Burning fossil fuels releases CO2 - as the world's become more industrialised, more fossil fuels have been burnt in power stations and in car engines
  • Deforestation - contributes to the increase in CO2 levels. Trees take in CO2 from the atmosphere, therefore getting rid of a whole load of trees means more CO2 is left in the atmosphere
  • Livestock farming - releases huge amouns of methane, CH4, into the atmosphere - animals produce it when they pass wind. The large population of dairy and beep cattle is to blame

Volcanic activity is changing the atmosphere:

  • Sulfur dioxide - thrown high into the atmosphere when volcanoes erupt, sulfur dioxide gas reacts with sunlight, water, oxygen and dust to form volcanic smog
  • Carbon dioxide - released into the atmosphere by volcanic eruptions
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