# Explain how the early atmosphere of the Earth changed to produce the atmosphere we have today, with reference to the role of photosynthesis and the formation of fossil fuels.

> Edexcel GCSE Chemistry (1CH0) — 8.2 Earth and atmospheric science · Explain · 4 marks

> Scientists believe the early atmosphere of the Earth was very different from the atmosphere we breathe today. Over billions of years, a series of processes changed the composition of the atmosphere dramatically.

## Mark scheme (4 marks)

1. The early atmosphere contained large amounts of carbon dioxide (and little or no oxygen).
2. Photosynthesis by plants and algae removed carbon dioxide from the atmosphere and produced oxygen.
3. The remains of ancient biomass (such as plankton) were buried in mud and over millions of years formed fossil fuels, locking carbon away from the atmosphere.
4. As a result, oxygen levels increased and carbon dioxide levels decreased, giving the atmosphere its current composition (approximately 21% oxygen and 0.04% carbon dioxide).

## Key terms

- [photosynthesis](https://www.gradenine.co.uk/glossary/photosynthesis)
- [fossil fuels](https://www.gradenine.co.uk/glossary/fossil-fuels)
- [atmosphere](https://www.gradenine.co.uk/glossary/atmosphere)

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" 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/explain-how-the-early-atmosphere-of-ce4f3132) · Published by Druglandscape Ltd.