1) Plants and plankton use carbon in the atmosphere for photosynthesis (CO2 + H2O -> C6H12O8 + O2).
2) Animals eat the plankton and plants, or decomposers/detritivores break down decaying plant material. This releases carbon back into the atmosphere via cellular respiration.
3) Dead organisms are buried and become fossil fuels, burned for fuel because of its carbon content (this returns carbon to the atmosphere)
