Geologists compare sedimentary rocks that formed at different times.
| Time when the rocks formed | Observations |
|---|---|
| 3.0 billion years ago | Large deposits of carbonate sediment formed on the sea floor. |
| 2.5 billion years ago | Banded iron formations were widespread in ocean sediments, but red iron oxide was not found in rocks formed on land. |
| 1.8 billion years ago | Banded iron formations were much less common, and red iron oxide was present in rocks formed on land. |
What change to the concentration of carbon dioxide in the Earth's atmosphere is supported by the carbonate sediments?
Explain your answer.
Explain what the observations of the iron-containing rocks suggest about the concentration of oxygen in the Earth's atmosphere between 2.5 and 1.8 billion years ago.
Suggest one reason why evidence from these rocks cannot show with certainty how the Earth's atmosphere changed.
109 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.