Geologists study how the Earth's early atmosphere became the atmosphere today. Their evidence includes three carbon stores.
| Carbon store | Evidence |
|---|---|
| Present atmosphere | Carbon dioxide makes up 0.04% of the gases. |
| Extensive limestone deposits | These contain carbon in carbonate sediments that formed in oceans. |
| Large coal seams | These contain carbon from buried organisms that took in carbon dioxide during photosynthesis. |
What do these carbon stores suggest about the early atmosphere?
Carbon in limestone and coal supports the idea that much more carbon dioxide was present in the early atmosphere.
The early atmosphere probably had about the same percentage of carbon dioxide as the atmosphere today.
Limestone and coal released their stored carbon to create the carbon dioxide in the early atmosphere.
The carbon in coal came from atmospheric carbon dioxide, but the carbon in limestone did not.
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.