The only source of carbon to produce organisms is the atmospheric carbon dioxide which is transformed from its gaseous state into carbohydrates and other organic materials by photosynthesis. Respiration of carbon dioxide by all organisms returns carbon to the atmosphere. Forest and grass fires also release carbon dioxide to the atmosphere. Carbon is deposited in soils and sequestered in sediments of streams, lakes, and oceans. Although the carbon cycle is simple the carbon exchanges through the food chain and the ocean surface waters are complex.
Prior to human intervention, the carbon flows in and out of the atmosphere may have been in equilibrium.
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