The carbon cycle

• The element carbon is found as carbon dioxide in the atmosphere, dissolved in the water of the oceans, as calcium carbonate in sea shells, in fossil fuels and in limestone rocks, and as carbohydrates and other large molecules in all living organisms.
• Carbon cycles through the environment by processes that include photosynthesis, respiration, combustion of fuels and the industrial uses of limestone.
• Life depends on photosynthesis in producers such as green plants, which make carbohydrates from carbon dioxide in the air.
• Animals feed on plants, passing the carbon compounds along food chains. Animals and plants respire and release carbon dioxide back into the air.
• Decay of dead plants and animals by microorganisms returns carbon to the atmosphere as carbon dioxide and mineral ions to the soil.