The global carbon cycle is what makes life on Earth possible. It is one of many Earth systems (including climate, the water cycle and the food web) that create a habitable environment for ourselves and millions of other species.

All life on earth, including humans, is based on carbon. Carbon is found the our bodies, in the oceans, in the air, and in the earth itself.

• In the atmosphere, carbon combines with oxygen (0₂) to form carbon dioxide (CO₂);
• In the oceans, carbon is processed by algae, one of the largest converters of oxygen to carbon dioxide;
• In plants, carbon becomes a carbohydrate, giving energy to the plant and eventually to the animals that eat the plant;
• In the earth, and in animal bones and shells, carbon forms calcium carbonate.

How does carbon cycle through the system?