The carbon cycle is the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere and atmosphere of the Earth. (Other bodies may have carbon cycles, but little is known about them.)
All of these components are reservoirs of carbon. The cycle is usually thought of as four main reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, terrestrial biosphere (usually includes freshwater systems), oceans, and sediments (includes fossil fuels). The annual mov ...
Carbon exists in Earth's atmosphere primarily as the gas carbon dioxide (CO2). Although it is a very small part of the atmosphere overall (approximately 0.04%, though rising), it plays an important role in supporting life. Other gases containing carbon in the atmosphere are methane and chlorofluorocarbons (the latter are entirely artificial). These are all greenhouse gases whose concentration in the atmosphere has been incr ...
