The table shows estimates of the percentage of oxygen in the Earth's atmosphere at different times.
| Time (billion years ago) | Oxygen in the atmosphere (%) |
|---|---|
| 4.0 | 0 |
| 3.0 | 0 |
| 2.0 | 2 |
| 1.0 | 5 |
| 0.4 | 20 |
| Today | 21 |
Fossils show that simple algae first appeared about 2.7 billion years ago and land plants about 0.47 billion years ago.
Which conclusion is best supported by this information?
Oxygen began to build up after algae evolved and rose fastest around the time land plants appeared.
Oxygen built up at a steady rate from the time the Earth formed until the present day.
Oxygen was released by volcanoes and built up before any algae had evolved.
Oxygen did not build up until land plants evolved, as they were the first to photosynthesise.
51 exam-style questions on OCR GCSE Chemistry 6.3 Interpreting and interacting with earth systems, covering 6.3.1 Formation and evolution of the atmosphere, 6.3.2 The greenhouse effect and climate change, 6.3.3 Sources and problems of atmospheric pollutants, and 6.3.4 Producing potable water. Each one has a worked solution and a mark scheme showing where the marks go.