The composition of Earth's atmosphere has evolved significantly over billions of years.
The table below shows the estimated percentages of carbon dioxide, nitrogen, and oxygen in Earth's early atmosphere compared to Earth's atmosphere today.
| Gas | Percentage (%) in Earth's early atmosphere | Percentage (%) in Earth's atmosphere today |
|---|---|---|
| Carbon dioxide (CO2\text{CO}_2CO2) | 95.095.095.0 | 0.040.040.04 |
| Nitrogen (N2\text{N}_2N2) | 4.04.04.0 | 78.078.078.0 |
| Oxygen (O2\text{O}_2O2) | Trace | 21.021.021.0 |
Explain how geological and biological processes caused the percentage of carbon dioxide in the atmosphere to decrease from 95.0%95.0\%95.0% to 0.04%0.04\%0.04%.
Explain how the percentage of oxygen in the atmosphere increased to its current level of 21.0%21.0\%21.0%.
Why are scientists not certain about the exact composition of Earth's early atmosphere?
7 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.