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GCSEChemistryAQARevision NotesChemistry of the AtmosphereFormation of Earth's AtmosphereHow Oxygen Increased

How Oxygen Increased (AQA GCSE Chemistry): Revision Note

Exam code: 8462

Stewart Hird

Last updated

AQA ChemistryAQA Combined Science: Trilogy: Chemistry

Why did oxygen levels increase?

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

  • 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

Photosynthesis word equation

  • The balanced symbol equation for photosynthesis is:

Balanced chemical equation for photosynthesis

  • Over billions of years, photosynthesis caused the amount of oxygen in the atmosphere to increase and the amount of carbon dioxide to decrease

  • This trend continued until around 200 million years ago when the composition of the atmosphere reached similar characteristics as today

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Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Content Creator

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.