Chemistry 1 Topic 1

Evolution of the atmosphere

Phase 1:

  • Volcanoes gave out gases as Earth's surface was molten.
  • Things cooled and a thin crust formed.
  • Volcanoes gave Carbon Dioxide and Water Vapour.
  • Early atmosphere was mostly CO2. Quite like Mars.
  • Oceans formed when water vapour condensed

Phase 2:

  • CO2 dissolved into oceans
  • Marine organisms developed. When they died they were buried under layers of sediment and the CO2 became locked up in carbonate rocks.
  • Green plants evolved over most of Earth, removed CO2 & produced oxygen by photosynthesis.

Phase 3:

  • Build of oxygen killed off some organisms
  • Oxygen created the ozone layer which blocked harmful rays from the sun.
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Today's atmosphere

Human activity:

  • Burning fossil fuels releases CO2.
  • Deforestation increases levels of CO2.
  • Livestock farming releases Methane.

Volcanic activity:

  • Sulfur dioxide gas reacts with sunlight, water, oxygen and dust - forming volcanic smog
  • Carbon dioxide is released by volcaninc eruptions

Sources of the evolution of the atmosphere are limited:

  • Learned a lot from Antartic ice cores.
  • Each year, a layer of ice forms and bubbles of air get trapped inside and then buried by the next layer.
  • The deeper the ice, the older the air.
  • If bubbles in different layers are examined carefully you can see how the air changed.
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Investigating the proportion of oxygen in the atmo

Here's an experiment to shoow the atmosphere contains around one fifth oxygen.

  • When it's heated, copper reacts with oxygen in the air to make copper (II) oxide - the reaction uses up oxygen.
  • If you heat an excess of copper in a tube and pass air over it using two syringes, you can use the markers to tell you how much oxygen has been used up.
  • If you start with 100cm*3 of air, you'll end up with about 80cm*3 when the reaction's finished. So about 20% of the air must be oxygen.
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