All topics › AQA GCSE Chemistry › How carbon dioxide decreased9.1.4 How carbon dioxide decreasedAQA GCSE Chemistry (8462), Higher tier · Chemistry of the atmosphere › Composition and evolution of the atmosphere
Practise How carbon dioxide decreased. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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The shells and skeletons of marine organisms are made mainly of one compound. calcium carbonate
Name the process by which plants and algae remove carbon dioxide from the atmosphere. photosynthesis
Calculate how many times greater the mass of carbon in the oceans is than the mass of carbon in fossil fuels. 9.5 Sample questions Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1 Easy 4 marks
(a) Give two ways in which the amount of carbon dioxide in the atmosphere was decreased.[2]
(b) Which rock was formed from the shells and skeletons of marine organisms?one box.[1]
Basalt Coal Granite Limestone (c) The shells and skeletons of marine organisms are made mainly of one compound.[1]
Show the answer and mark scheme (a) photosynthesis by algae and plants dissolving in the oceans formation of sedimentary rocks / carbonates formation of fossil fuels (b) Answer: Limestone
(c) Answer: calcium carbonate
Question 2 Medium 6 marks
Coal, crude oil and natural gas are fossil fuels. They contain carbon that was once in the atmosphere as carbon dioxide.
(a) Describe how coal was formed.[2]
(b) Describe how crude oil and natural gas were formed.[2]
(c) Explain how the formation of coal reduced the amount of carbon dioxide in the atmosphere.[2]
Show the answer and mark scheme (a) from the remains of plants (that lived millions of years ago) buried and compressed over millions of years (without oxygen) (b) from the remains of plankton / tiny sea organisms buried in mud heat and pressure over millions of years (without oxygen) (c) plants took in carbon dioxide for photosynthesis the carbon was locked up in the coal instead of returning to the atmosphere (when the plants decayed) Question 3 Hard 6 marks
The Earth's atmosphere today is very different from the Earth's early atmosphere.
Describe the main changes in the Earth's atmosphere from the early atmosphere to the atmosphere today.[6]
Show the answer and mark scheme early atmosphere was mainly carbon dioxide with little or no oxygen; today about 80% nitrogen, 20% oxygen and about 0.04% carbon dioxide carbon dioxide dissolved in the oceans and carbonates were precipitated, forming sediments algae (from about 2.7 billion years ago) and later plants photosynthesised, using carbon dioxide and releasing oxygen oxygen gradually increased to a level that enabled animals to evolve limestone formed from the shells and skeletons of marine organisms (calcium carbonate) coal formed from the remains of plants; crude oil and natural gas formed from plankton buried in mud so carbon was locked up in sedimentary rocks and fossil fuels nitrogen released by volcanoes gradually built up because it is unreactive Marked with levels of response: the full level descriptors are in the app.
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