GCSE Chemistry revision

How oxygen increased

The composition and evolution of the Earth's atmosphere

AQA 4.9.1.3 Foundation & Higher

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Around 2.7 billion years ago, algae began to appear, followed by green plants, both of which are capable of photosynthesis.
Photosynthesis removes carbon dioxide from the atmosphere and releases oxygen, gradually reducing CO₂ levels and increasing oxygen levels over billions of years.
The build-up of oxygen in the atmosphere eventually allowed more complex life forms, such as animals, to evolve.

1. The Role of Algae and Green Plants AQA

Around 2.7 billion years ago, algae began to appear, followed by green plants, both of which are capable of photosynthesis.
Photosynthesis removes carbon dioxide from the atmosphere and releases oxygen, gradually reducing CO₂ levels and increasing oxygen levels over billions of years.
The build-up of oxygen in the atmosphere eventually allowed more complex life forms, such as animals, to evolve.

Rise of Oxygen Levels: The evolution of photosynthetic organisms, beginning with primitive algae around 2.7 billion years ago, gradually increased atmospheric oxygen concentrations while consuming carbon dioxide.
Example: The overall equation for photosynthesis shows how algae transformed carbon dioxide into oxygen:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

2. Rise of Oxygen Levels AQA

Rise of Oxygen Levels: The evolution of photosynthetic organisms, beginning with primitive algae around 2.7 billion years ago, gradually increased atmospheric oxygen concentrations while consuming carbon dioxide.
Example: The overall equation for photosynthesis shows how algae transformed carbon dioxide into oxygen:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Carbon dioxide levels further dropped as carbon was incorporated into the tissues of plants and aquatic organisms, which eventually died and became buried under high pressure.
Example: Ancient marine organisms deposited on the sea bed were buried by sediment over millions of years, turning into crude oil and natural gas and locking carbon underground.

3. Carbon Storage in Fossil Fuels AQA

Carbon dioxide levels further dropped as carbon was incorporated into the tissues of plants and aquatic organisms, which eventually died and became buried under high pressure.
Example: Ancient marine organisms deposited on the sea bed were buried by sediment over millions of years, turning into crude oil and natural gas and locking carbon underground.