Earth's Early Atmosphere

This lesson covers the Earth's early atmosphere as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand what the early atmosphere was like, where it came from, and how the oceans formed.

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How Did the Atmosphere Form?

The Earth is approximately 4.6 billion years old. During the first billion years, there was intense volcanic activity. Scientists believe the early atmosphere was formed by volcanic degassing — gases released from volcanoes.

Evidence from Other Planets

We cannot directly sample Earth's ancient atmosphere, but we can look at the atmospheres of other rocky planets:

• Venus and Mars both have atmospheres rich in carbon dioxide (about 95–96% CO₂).
• Scientists believe Earth's early atmosphere was similar — mostly CO₂ with some other volcanic gases.

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Composition of the Early Atmosphere

The early atmosphere (around 4–3.5 billion years ago) was very different from today: