The table shows the percentage of three gases in the Earth's atmosphere at four times in the past.
Table: The percentage of carbon dioxide, oxygen and nitrogen in the Earth's atmosphere at four times in the past
| Time / billions of years ago | Carbon dioxide (%) | Oxygen (%) | Nitrogen (%) |
|---|---|---|---|
| 4.0 | 90 | 0 | 5 |
| 3.0 | 70 | 0 | 20 |
| 2.0 | 20 | 2 | 70 |
| 1.0 | 1 | 12 | 80 |
Use the table. Between which two times did photosynthesis first become a cause of the changes in the gases?
4.0 and 3.0 billion years ago
3.0 and 2.0 billion years ago
2.0 and 1.0 billion years ago
1.0 billion years ago and today
40 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.