Biology - The Carbon Cycle

It is quite possible that your body contains carbon atoms that were once breathed by a dinosaur. Or perhaps eaten by a king or queen or even excreted in dog poo. Yeuch! But how is this possible? The answer is one of the most important cycles for life - the carbon cycle. Our planet has only a limited stock of chemical elements and they are constantly being recycled in different ways. If they weren't, they would all have been used up long ago and the Earth would be an unchanging dead planet.

When looking at the carbon cycle, it doesn't really matter where you start. A good place to start though is with the carbon dioxide in the air. This is absorbed by plants and used by them to produce biomass. The carbon in the plants then enters into food chains. When a plant is eaten by an animal, the carbon is passed on. The animal may use the carbon from the plant to make its own biomass, in which case it will be locked up until the animal dies. It could be used in respiration to generate energy, in which case, the carbon ends up back as carbon dioxide in the air. If the carbon is excreted as waste material, the decomposers will either release it back into the air as carbon dioxide straight away or lock it up inside their bodies as biomass.

And so it goes on, constantly being exchanged between plants, animals and the air. But food chains are not the only places where carbon is stored. It can even be locked away in rocks like limestone and chalk, only to be released millions of years later when molten magma touches them. Or it can be fossilized, as coal or oil, and released when it is burnt to generate energy.