The coal is then burned to produce electricity, and thus the carbon is returned to carbon dioxide in the air.
Aquatic and marine plants absorb dissolved carbon dioxide from the atmosphere to photosynthesize. The dissolved carbon dioxide is also converted in carbonates and bicarbonates. After long periods of time, these deposits are returned to the lithosphere as sedimentary rocks.
Secondly, Nitrogen is another element that plays important roles in both biological and non-biological systems. Nitrogen gas makes up 80% of the Earth's atmosphere and nitrogen exists in proteins of living organisms.
Through nitrogen fixation, part of the nitrogen gas is converted to ammonia, ammonium and nitrates ions where are the primary sources of nitrogen compounds to all living things. These nitrogen compounds absorbed are subsequently used in the production of proteins in plants and animal. After consumption of plants and other animals, animals release ammonia to the atmosphere through excretion. Also, both the plant and animals proteins can be broken down and digested by microbes once the plant or animal dies into ammonia. This ammonia is then oxidized by nitrifying bacteria into nitrites, which are then oxidized again by other nitrifying bacteria into nitrates. Denitrifying bacteria can reduce nitrates to nitrogen in the air, nitrites or ammonia. .
Thirdly, another major biogeochemical cycle of significance to climate and life is the sulphur cycle. Relatively low level of sulphur is required for the production of proteins in all living things. The original pool of sulphur on Earth was held in igneous rocks, but today, the major global pools of sulphur are found in sedimentary pyrite, seawater and evaporates derived from ocean water. The sulphur in the atmosphere comes from the lithosphere through volcanic activities and a portion is the product of combustion of fossil fuels. Sulphate (SO42-), derived from the weathering and oxidation of rocks, is taken up by plants and incorporated into sulphur-containing proteins.
