Oxygen is one of the gases in the Earth’s atmosphere today. The percentage of oxygen in the Earth’s atmosphere has changed significantly over geological time.
Which row in the table shows the approximate percentage of oxygen thought to be present in the Earth’s early atmosphere and how this percentage changed over time to form the atmosphere we have today?
| Approximate percentage of oxygen in the early atmosphere | Change in oxygen percentage over time to today | |
|---|---|---|
| A | < 1% | increased |
| B | < 1% | decreased |
| C | 21% | increased |
| D | 21% | decreased |
Row A
Row B
Row C
Row D
97 exam-style questions on Edexcel GCSE Chemistry 9.2 Earth and atmospheric science, covering 9.2.1 The Earth's early atmosphere, 9.2.2 How the atmosphere evolved, 9.2.3 Chemical test for oxygen, and 9.2.4 The greenhouse effect and climate change. Each one has a worked solution and a mark scheme showing where the marks go.