The Carbon Cycle main content.

The Carbon Cycle

Part of Hall of Planet Earth.

The Carbon Cycle AMNH/R.Mickens

Carbon is a major component of all life, and in the form of the greenhouse gas carbon dioxide, it helps to maintain a habitable range in temperatures. Carbon moves through all the Earth’s reservoirs. Most of it is contained in sedimentary rocks: coal, chalk, lime-stone, and shale. But carbon in sedimentary rocks, with an average residence time of 400 million years, participates little in global carbon circulation over shorter times. The average residence times of carbon in the atmosphere (5 years), the biosphere (13 years), and the oceans (350 years) are much shorter.