A geologist examines layers exposed in a cliff after a landslip. Fig. 1 shows a simplified cross-section. The lowest layer contains coal, a black solid rich...
Question 1 Report
A geologist examines layers exposed in a cliff after a landslip. Fig. 1 shows a simplified cross-section. The lowest layer contains coal, a black solid rich in carbon. Above it are sedimentary rocks, soil and modern plants. Coal formed from ancient plant material buried before it could decay fully. A nearby power station burns coal in a reaction with oxygen to release energy for electricity. Local residents are planting trees on the old mine site and want to understand whether this can affect the carbon cycle.
(a) Name the process that removed carbon dioxide from the atmosphere when the ancient plants were alive. [2]
(b) Describe how the carbon in ancient plants became stored in the coal seam. [3]
(c) Use Fig. 1 to explain why coal is described as a non-renewable fuel on a human timescale. [3]
(d) Explain how burning coal and planting trees have opposite effects on the amount of carbon dioxide in the atmosphere. [4]
Answer Details
(a) Photosynthesis by plants [2] removed carbon dioxide from the atmosphere when the ancient plants were alive.
(b) [3] Dead plants were buried beneath layers of sediment. Little oxygen limited complete decay. Over a very long period, heat and pressure changed the plant material into coal.
(c) [3] The coal is shown in a deep, old layer below sedimentary rock. It formed over millions of years, much longer than a human lifetime. It cannot be replaced as quickly as it is extracted and used, so it is non-renewable on a human timescale.
(d) [4] Burning coal is combustion, a reaction with oxygen. Carbon in the coal is converted to carbon dioxide, adding carbon dioxide to the atmosphere. Trees have the opposite effect because they remove carbon dioxide by photosynthesis and store carbon in biomass.
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