Scientists estimate the proportions of two gases in the atmosphere at two stages.
| Stage | Oxygen (% by volume) | Carbon dioxide (% by volume) |
|---|---|---|
| Earlier stage | 0.5 | 18 |
| Later stage | 21 | 0.04 |
Describe how the proportions of the two gases changed between the two stages, and explain the processes that caused these changes.
79 exam-style questions on AQA GCSE Chemistry 9.1 The composition and evolution of the Earth's atmosphere, covering 9.1.1 The proportions of different gases in the atmosphere, 9.1.2 The Earth's early atmosphere, 9.1.3 How oxygen increased, and 9.1.4 How carbon dioxide decreased. Each one has a worked solution and a mark scheme showing where the marks go.