A scientist develops two computer models of an atmosphere above an ocean. The models include only carbon dioxide, oxygen and nitrogen.
Both models begin with the same atmosphere and allow carbon dioxide to dissolve in the ocean and form carbonates. They also allow oxygen to react with dissolved iron and material from dead organisms to be buried. Neither model adds or removes nitrogen.
Model L contains no living organisms. Model P contains photosynthesising algae. The table shows the results after the same simulated time.
| Gas | Amount in Model L (× 10¹⁸ mol) | Amount in Model P (× 10¹⁸ mol) |
|---|---|---|
| carbon dioxide | 45 | 12 |
| oxygen | 0 | 18 |
| nitrogen | 30 | 30 |
Compare the amounts of carbon dioxide and oxygen in the two models. Explain how the algae cause these differences.
Calculate the percentage of nitrogen in the atmosphere predicted by each model. Explain why the percentage is greater in Model P even though both models contain the same amount of nitrogen.
The atmosphere today is about 78% nitrogen, 21% oxygen and 0.04% carbon dioxide.
Evaluate whether Model P gives a complete explanation for the composition of the atmosphere today. Use the data in your answer.
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.