9.1.2

Oxygen & Carbon Dioxide in the Atmosphere

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The Rise of Oxygen in the Earth's Atmosphere

Photosynthesis increased the atmospheric concentration of oxygen.

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What is photosynthesis?

  • Photosynthesis is the process in which light energy is used to produce glucose and oxygen from carbon dioxide and water.
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Photosynthetic organisms

  • Algae were the first photosynthetic organisms to evolve. This happened about 2.5-2.7 billion years ago.
  • Photosynthesising plants then began to evolve over the next billion years. This led to an ever-increasing rate of oxygen accumulating in the atmosphere.
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The evolution of more complex organisms

  • More complex life forms, such as animals, began to evolve once a threshold concentration of oxygen was reached.

The Decrease in Atmospheric Carbon Dioxide

At least 3 factors caused atmospheric carbon dioxide to decrease:

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Oceans

  • The formation of oceans removed large amounts of carbon dioxide from the atmosphere.
  • Once dissolved in the oceans, some of this carbon dioxide reacted with seawater to give carbonate precipitates.
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Photosynthesis

  • Carbon dioxide is one of the reactants of the equation for photosynthesis.
  • So, the photosynthetic action of algae and plants removed carbon dioxide from the atmosphere.
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Marine animals

  • The evolution of marine animals removed carbonates from the oceans as the animals used these to build their shells and skeletons.

Jump to other topics

1Atomic Structure

2Chemical Bonding

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

6The Rate & Extent of Chemical Change

7Organic Chemistry

8Chemical Analysis

9Chemistry of the Atmosphere

10Using Resources

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