Evolution of the atmosphere
- 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
- 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.
- Build of oxygen killed off some organisms
- Oxygen created the ozone layer which blocked harmful rays from the sun.
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- Burning fossil fuels releases CO2.
- Deforestation increases levels of CO2.
- Livestock farming releases Methane.
- 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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