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| Carbon Cycle |
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| Carbon is found as graphite and diamond in nature. It also occurs as carbon dioxide in the atmosphere. |
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| Because of the position of its electrons, an atom of carbon can form covalent bonds with hydrogen, oxygen, nitrogen, phosphorus and other carbon atoms. Because of this versatility, the carbon atom is the principal building block of many kinds of molecules, which make up the living organisms. |
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| Carbon cycle is a perfect cycle in the sense that carbon is returned to atmosphere as soon as it is removed. |
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| Sources of Carbon |
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| 1) Major source of carbon for the living world is carbon dioxide. Atmosphere contains about 700 x 109 metric tonnes of carbon dioxide while ocean water contains about 35,000 x 109 metric tonnes of carbon dioxide. |
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| 2) Carbonates of earth's crust derived from rocks, which by chemical reactions give rise to carbon dioxide. |
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| 3) Fossil fuels like peat, coal and petroleum products found in the lithosphere contains about 2.81 x 1021 kg of carbon |
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| 4) Oceans, where carbon remains stored as carbonates in the form of limestone and marble rocks. |
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| Carbon dioxide utilization |
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| The major process that brings carbon form the atmosphere into the living world is photosynthesis, where producers take in carbon dioxide from the atmosphere and convert it into organic compounds. Oxygen is released as a by product. |
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| Carbon fixed by the producers enters the food chain and is passed to herbivores, carnivores and decomposers. |
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| Carbon dioxide production |
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| a) Carbon dioxide is released back to the environment by respiration of producers and consumers |
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| b) Released by the decomposition of organic wastes and dead bodies by the action of bacteria and fungi on decay. |
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| c) Burning of wood and fossil fuels add considerable amount of carbon dioxide into the atmosphere |
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| d) Volcanic eruptions and weathering of carbonate rocks by the action of acids |
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| The estimated amount of carbon fixed by photosynthesis is nearly 7 x 1013 kg / year. |
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| A large number of organisms buried deep in the layers of the earth, transform into coal, petroleum and natural gas, remains locked up till man uses them. Thus, natural exchange between lithosphere and hydrosphere or atmosphere is a slow process and is a self regulated feed back system. |
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| Recently this self regulated system has been upset by man's activities such as large scale deforestation and excessive burning of fossil fuels. As a result, carbon dioxide content of the atmosphere is increasing, affecting the green house effect in nature. |
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| Green house is usually a type of glasshouse used for raising tender plants. Air inside the green house is usually warmer than the outside, though it receives less solar radiation due to the carbon dioxide present inside, produced by plants (by respiration). This is called 'green house effect'. |
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| In nature, gases like carbon dioxide, methane and water vapour are called 'green house gases' because these absorb the long wavelength infrared radiations emitted by the earth's surface. Dust and clouds also prevent the dissipation of these heat radiations, so also exert green house effect. |
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| Certain human activities have resulted in increased production of carbon dioxide leading to its increased concentration in the atmosphere. This has lead to disturbances in the climatic conditions of the environment and has caused conditions which may melt away polar as well as alpine ice resulting in 18 - 20 metres rise in sea level and submerge vast areas of land. |
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