The greenhouse effect and concern about climate change has made carbon a celebrity. Terms such as carbon trading, and carbon credits are now familiar to all of us, but what is carbon and why is it important?
Carbon is an abundant non-metallic element that forms the chemical basis for all known life. In chemistry carbon is symbolised as C. The carbon atom has 6 electrons, 2 in the nucleus of the atom and 4 in the valence shell, consequently carbon has an atomic mass of 6 and a valency of 4. Valency can be thought of as hooks which an atom can use to hang on to other atoms It is carbon’s atomic structure which is the key to its importance, because the carbon atom can form stable covalent bonds with other carbon atoms and form chains with a wide variety of other elements. So far we know of 10 million compounds. The large majority of known compounds are organic ie contain carbon. Carbon can also form allotropes, the same element with different physical structure eg naturally occurring carbon includes diamond – the hardest known natural substance and graphite (used in lead pencils) one of the softest.
To realise the importance of carbon to all life consider some of the following carbon compounds:
Carbon dioxide – essential to plant photosynthesis; Hydrocarbons – flammable compounds that are used to produce energy eg coal and oil; Carotenoids and terpenes which are living plant components; Biological compounds such as cellulose, sugars, carbohydrates, alcohol, fats, esters, alkaloids, proteins, amino acids and also DNA and RNA which provide the blueprint for life. On average the human body is 19% carbon (2nd after oxygen which makes up 63% of our bodies)
Carbon was identified by people from prehistoric times; the word carbon is derived from the Latin word for coal, carba. In the 1850s chemists started to make organic compounds from air, water and coal, this process, called synthesis, laid the groundwork for the development of more complex synthetic carbon compounds. A huge array of synthetic materials now exist - alcohol, dyes, perfumes, drugs such as heroin and barbiturates, anaesthetics, explosives, polymers, plastics and synthetic fibres are all derived from carbon.
The carbon cycle is a complex system of rotating the Earth’s carbon atoms. The same carbon atoms in your body have had many owners before you, in fact they have been recycled countlessly through the living and the dead, the animate and inanimate, since the earth began – rocks, dinosaurs, plants, oceans, insects, carrion, waste, fish, cavemen - you name it, they have all used your carbon before you.
There are 4 major reservoirs of carbon – biosphere (living things), geosphere (earth), hydrosphere (water) and atmosphere (air). A number of chemical, physical, geological and biological processes form pathways of exchange between the reservoirs. Eg plants absorb carbon dioxide during photosynthesis, and produce carbohydrates which are consumed by animals (atmosphere to biosphere), forests are eventually converted to coal, gas and oil (biosphere to geosphere), the oceans absorb carbon dioxide from the air (atmosphere to hydrosphere) and the most topical, burning of fossil fuels releases carbon dioxide into the atmosphere (geosphere to atmosphere).
The Earth is a complex entity and human understanding of its processes is far from comprehensive, but one thing is certain, life as we know it depends on the carbon cycle.