Carbon cycle
The carbon cycle is a process where carbon is recycled through the ecosystem. The concentration of carbon in living matter (18%) is almost 100 times greater than its concentration in the earth (0.19%). So living things extract carbon from their nonliving environment. For life to continue, this carbon must be recycled. See the diagram for a detailed look at the carbon cycle. An example of a route carbon takes in this cycle is carbon dioxide in the atmosphere is absorbed by plants and used in photosynthesis to produce sugars which the plant uses for energy. When the plant dies, it decomposes and the carbon stored in the plant will, over millions of years, form into coal (a fossil fuel). The coal is burnt and gives off carbon dioxide which goes into the atmosphere.