carbon cycle

American  

noun

1. Ecology. the circulation of carbon atoms in the biosphere as a result of photosynthetic conversion of carbon dioxide into complex organic compounds by plants, which are consumed by other organisms: the carbon returns to the atmosphere in the form of carbon dioxide as a result of respiration, decay by fungi, bacteria, etc., and combustion of fossil fuels.

2. Astrophysics. a cycle of nuclear transformations in the interiors of the stars by means of which hydrogen is gradually converted into helium with the release of nuclear energy.

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carbon cycle British  

noun

1. the circulation of carbon between living organisms and their surroundings. Carbon dioxide from the atmosphere is synthesized by plants into plant tissue, which is ingested and metabolized by animals and converted to carbon dioxide again during respiration and decay

2. four thermonuclear reactions believed to be the source of energy in many stars. Carbon nuclei function as catalysts in the fusion of protons to form helium nuclei

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carbon cycle Scientific  

1. 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.

2. 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.

3. Also called Bethe cycle carbon-nitrogen cycle

4. See also proton-proton chain triple alpha process

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carbon cycle Cultural  

1. In ecology, the movement of atoms of carbon through the biosphere. Molecules of carbon dioxide are taken in by plants, to be incorporated into their tissues, which may then be eaten by and incorporated into animals. Animals return the carbon to the air in the form of carbon dioxide, and the cycle starts again. (See photosynthesis and respiration.)

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Etymology

Origin of carbon cycle

First recorded in 1910–15

Example Sentences

"How much DOC finds its way to the ocean via rivers and streams is a part of the carbon cycle we don't know much about," says Rawlins.

From Science Daily • Apr. 4, 2026

Tropical swamps and peatlands are critical players in Earth's carbon cycle and, by extension, the global climate.

From Science Daily • Feb. 24, 2026

"This study revealed the importance of such breccia, which forms due to the erosion of seafloor mountains along mid-ocean ridges, as a sponge for carbon in the long-term carbon cycle."

From Science Daily • Dec. 11, 2025

The Southern Ocean is a major regulator of the global carbon cycle, absorbing a large share of the carbon released by human activity.

From Science Daily • Nov. 8, 2025

"Well, I understand that both oxygen and hydrogen are furnished by natural processes, the oxygen from carbon dioxid in the carbon cycle, and the hydrogen from the water which falls in rain."

From The Story of the Soil; from the Basis of Absolute Science and Real Life, by Hopkins, Cyril G. (Cyril George)