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This lesson covers how Earth's atmosphere changed over time from being rich in CO₂ to the nitrogen-and-oxygen atmosphere we have today, as required by the Edexcel GCSE Combined Science specification (1SC0). The key process is photosynthesis by early organisms.
Before understanding how the atmosphere evolved, you need to know what it looks like now:
| Gas | Approximate Proportion |
|---|---|
| Nitrogen (N₂) | 78% |
| Oxygen (O₂) | 21% |
| Argon (Ar) | ~0.9% |
| Carbon dioxide (CO₂) | ~0.04% |
| Water vapour | Variable (0–4%) |
Compare this with the early atmosphere:
The oxygen in our atmosphere was produced by photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
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