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carbon cycle science definition
- The continuous process by which carbon is exchanged between organisms and the environment. Carbon dioxide is absorbed from the atmosphere by plants and algae and converted to carbohydrates by photosynthesis. Carbon is then passed into the food chain and returned to the atmosphere by the respiration and decay of animals, plants, and other organisms. The burning of fossil fuels also releases carbon dioxide into the atmosphere.
- A cycle of thermonuclear reactions caused by the absorption of protons by the nucleus of a carbon-12 atom, in which helium and isotopes of nitrogen, carbon, and oxygen are produced, and resulting in the regeneration of a carbon-12 atom so that the process can begin again. The carbon cycle is thought to be the source of significant amounts of energy in the Sun and other stars. Also called Bethe cycle, carbon-nitrogen cycle. See also proton-proton chain, triple alpha process.
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