GCSE Combined Science (AQA)

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The Early Atmosphere: Oxygen

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Chemistry of the atmosphere The composition and evolution of the Earth's atmosphere

The Early Atmosphere: Oxygen

2:30 Changes in Earth's Atmosphere Over Time
Spec 4.9.1.3
Previous The Early Atmosphere Next The Early Atmosphere: Carbon Dioxide
  • The Earth's early atmosphere had little or no oxygen.
  • Earth is about 4.6 billion years old.
  • Early atmosphere was mostly carbon dioxide with some nitrogen and water vapor due to volcanic eruptions.
  • Water vapor condensed to form oceans, reducing carbon dioxide and increasing oxygen in the atmosphere.
  • Algae and plants produced the oxygen present in the atmosphere today.
  • Algae first produced oxygen about 2.7 billion years ago through photosynthesis.
  • Cyanobacteria were among the first organisms to photosynthesize and were early life forms on Earth.
  • Photosynthesis equation: Carbon dioxide + water + light ��� glucose + oxygen.
  • Symbol equation: 6 CO2 + 6 H2O ��� C6H12O6 + 6 O2.
  • Light is essential for photosynthesis, driving the endothermic reaction that produces glucose.
  • Over a billion years, plants evolved, increasing atmospheric oxygen.
  • More complex life forms evolved as oxygen levels increased.
  • More plants led to more photosynthesis, further increasing atmospheric oxygen.
  • Oxygen levels eventually enabled animal evolution.

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