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.
Practise Edexcel GCSE Chemistry Earth and atmospheric science with exam-style questions for Foundation and Higher tier. 62 questions, matched to the Edexcel GCSE Chemistry (1CH0) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
