THE CARBON CYCLE describes the biogeochemical cycle, or routes by which carbon atoms are exchanged through nested networks of environmental systems from the atmosphere into the biosphere, through photosynthesis and back again with respiration, decomposition, and biomass burning. Elemental carbon is a traditional component of the hydrosphere, the atmosphere, the geosphere (rocks, such as limestone; coal; and soils), as well as the biosphere (all living things).

The carbon cycle also involves the process of removal and uptake of carbon on a global scale. This process involves components in food chains, in the atmosphere, as carbon dioxide; in the hydrosphere; and in the geosphere. The major movement of carbon results from photosynthesis and from respiration. Carbon is present in the planet in the following major reservoirs: as ...