carbon cycle

noun

• 1 Biochemistry the series of processes by which carbon compounds are interconverted in the environment, chiefly involving the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels.

• 2 Astronomy the cycle of thermonuclear reactions believed to occur in stars, in which carbon nuclei are repeatedly formed and broken down in the conversion of hydrogen into helium.