The key structural element of life keeps cycling on several spatial and temporal scales, ranging from virtually instantaneous returns to circulations that take 108 years to complete. At one extreme are very rapid assimilationÃ¢â‚¬â€œrespiration flows between the plants and the atmosphere and less rapid but still fast assimilationÃ¢â‚¬â€œdecompositionÃ¢â‚¬â€œassimilation circuits that move the element from the atmosphere to plant tissue of various ecosystems and return it to the atmosphere after carbon's temporary stores in dead organic matter (in surface litter and soils) are mineralized by decomposers (Fig. 3). The other extreme involves slow weathering of terrestrial carbonates, their dissolution, river-borne transport, and eventual sedimentation in the ocean, and the element's return to land by geotectonic processes. Human interest in the cycle is due not only to the fact that carbon's assimilation through photosynthesis is the foundation of all but a tiny fraction of the earth's life but also to the cycle's sensitivity to anthropogenic perturbations.
Read this topic