Carbon is one of the most important constituent of all organic compounds. It is the building block of life. Carbon is an essential constituent of carbohydrates, proteins, fats, and nucleic acids. The main reservoirs of carbon are:
- Atmosphere, in which carbon is present as carbon dioxide.
- Oceans, in which carbon is present as carbon dioxide dissolved in water. In addition, it is also present as calcium carbonate in various seashells and in rocks at the bottom of sea.
- Land, on which it is present in some ores like dolomite and other
The carbon cycle (or the so called carbon dioxide cycle) involves the circulation of carbon dioxide from the three sources as shown below in Fig
The carbon or the carbon dioxide cycle involves the following process a Carbon dioxide from the atmosphere enters the plant through photosynthesis, where carbonhydrates are produced.
From green plants, the carbon in the form of carbohydrates, etc., enter the animal and human bodies.
The remains of dead animals and plants on putrification and bacterial decomposition release carbon dioxide back into the atmosphere.
The atmospheric carbon dioxide gets dissolved in oceans, etc., by simple diffusion process. Marine algae and photosynthetic bacteria obtain carbon dioxide from water. Some of the dissolved carbon dioxide is also trapped to form lime stone (calcium carbonate) and other carbonate containing
Carbon dioxide returns to the atmosphere by respiration, combustion of fossil fuels like coal, wood, petroleum, diesel, natural gas, gasoline
Weathering of carbonate containing rocks (particularly by water containing dissolved carbon dioxide as carbonic acid and by acid rain) releases carbon dioxide into the atmosphere. Carbon dioxide is also released into the atmosphere by volcanic eruptions.