Production of Oxygen by Photosynthesis

  • Primitive plants and algae began photosynthesizing which used up CO2 from the atmosphere and released oxygen:

6CO2 + 6H2O → C6H12O6 + 6O2

  • Through these processes and over a long period of time, the amount of O2 in the atmosphere increased and the amount of CO2 decreased, being trapped in fossil fuels and sedimentary rocks.
  • Algae first evolved around 2.7 billion years ago and during the next billion years or so small green plants began to appear.
  • As more and more plants began to appear the levels of oxygen began to increase which allowed for more complex life forms to evolve.
  • This trend continued until around 200 million years ago the composition of the atmosphere reached similar characteristics as today: around 20% oxygen, 80% nitrogen and tiny amounts of other gases.

AQA GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.