At a standard atmospheric pressure of 100 kPa, modern dry air contains approximately 78.08% nitrogen, 20.95% oxygen, 0.93% argon, and 0.04% carbon dioxide by volume.
Which of the following options correctly identifies the approximate partial pressure of carbon dioxide (pCO2p_{\text{CO}_2}pCO2) in modern dry air and the primary historical sink that removed the vast majority of carbon dioxide from the Earth's early atmosphere?
pCO2≈400 Pap_{\text{CO}_2} \approx 400 \text{ Pa}pCO2≈400 Pa, and the primary long-term sink was the burial of organic matter to form fossil fuels.
pCO2≈40 Pap_{\text{CO}_2} \approx 40 \text{ Pa}pCO2≈40 Pa, and the primary long-term sink was the dissolution of CO2\text{CO}_2CO2 in the oceans followed by precipitation as sedimentary carbonate rocks.
pCO2≈40 Pap_{\text{CO}_2} \approx 40 \text{ Pa}pCO2≈40 Pa, and the primary long-term sink was solar-wind-induced escape of volatile gases into outer space.
pCO2≈4000 Pap_{\text{CO}_2} \approx 4000 \text{ Pa}pCO2≈4000 Pa, and the primary long-term sink was the direct mineralisation of gaseous CO2\text{CO}_2CO2 into igneous silicate minerals.
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.