Carbon cycle

flow of carbon between living organisms and environment; thermonuclear reaction in the interior of stars

. The carbon cycle is the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth.The cycle is usually thought of as four major reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, the terrestrial biosphere (which usually includes freshwater systems and non-living organic material, such as soil carbon), the oceans (which includes dissolved inorganic carbon and living and non-living marine biota), and the sediments (which includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth, but the deep ocean part of this pool does not rapidly exchange with the atmosphere.
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Noun
1. the organic circulation of carbon from the atmosphere into organisms and back again
(hypernym) organic process, biological process
2. a thermonuclear reaction in the interior of stars
(hypernym) thermonuclear reaction

All carbon reservoirs and exchanges of carbon from reservoir to reservoir by various chemical, physical, geological, and biological processes. Usually thought of as a series of the four main reservoirs of carbon interconnected by pathways of exchange. The four reservoirs, regions of the Earth in which carbon behaves in a systematic manner, are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). Each of these global reservoirs may be subdivided into smaller pools, ranging in size from individual communities or ecosystems to the total of all living organisms (biota).

A sequence of six sequential nuclear fusion events in which a helium nucleus is formed from four hydrogen nuclei, via a reaction which uses a carbon nucleus as a catalyst. Along the way, the carbon is converted into isotopes of nitrogen and oxygen, before being returned to its original form in the final stage of the reaction having acted as a catalyst. This cycle, also known as the carbon-nitrogen, or carbon-nitrogen-oxygen (CNO) cycle, takes place at temperatures greater than four million degrees Kelvin . It is the predominant way in which helium is produced in stars which are several times more massive than the Sun. See also proton-proton chain.