AQA GCSE Chemistry

Revision Notes

9.1.3 How Oxygen Increased

Production of Oxygen by Photosynthesis

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

Photosynthesis word equation, IGCSE & GCSE Biology revision notes

Carbon dioxide and water producing glucose and oxygen during photosynthesis

  • Through these processes over a long period of time, the amount of O2 in the atmosphere increased  and the amount of CO2 decreased
  • 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
  • Marine algae are throught to be responsible for about 90% of all the atmospheric oxygen produced

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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