# Describe how the Earth's early atmosphere changed over billions of years to produce an atmosphere that contains mainly nitrogen and oxygen.

> Eduqas GCSE Chemistry — C9 Chemistry of the atmosphere · Describe · 4 marks

## Mark scheme (4 marks)

1. The early atmosphere was mainly carbon dioxide (and water vapour / small amounts of other gases such as methane or ammonia)
2. Water vapour condensed to form the oceans, and carbon dioxide dissolved in the oceans (reducing CO₂ levels)
3. Photosynthesis by plants/algae/microorganisms removed carbon dioxide and released oxygen
4. Nitrogen levels increased over time as it was released by volcanic activity and/or bacteria, and nitrogen is unreactive so it accumulated

## Key terms

- [early atmosphere](https://www.gradenine.co.uk/glossary/early-atmosphere)
- [nitrogen](https://www.gradenine.co.uk/glossary/nitrogen)
- [oxygen](https://www.gradenine.co.uk/glossary/oxygen)

## Related

- [Revision notes for Eduqas GCSE Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-the-earth-s-early-atmosphere-e2702ea2) · Published by Druglandscape Ltd.