 
Carbon is a chemical element with atomic number 6; classified as a nonmetal, carbon is a solid at room temperature. Essential to life, it is the fourth most abundant element in the universe, after hydrogen, helium and oxygen. Carbon makes up around half of the mass of trees and plants. It's the second most abundant element in the human body after oxygen, making up about 18.54% of human body mass and a similar percentage in all living creatures. There are a number of pure forms of the element carbon, including graphene, diamond, fullerenes and graphite. 
Graphene is made of a single sheet of carbon atoms arranged in a crystal lattice like a honeycomb. It is one atom thick and two-dimensional, composed of carbon atoms joined by covalent bonds. It has been described the world's strongest material, as it is over 200 times stronger than steel, as well as being lightweight and flexible. Graphene is both highly conductive and transparent.
Graphite is black and shiny, but soft. Graphite is a crystalline form of carbon consisting of stacked layers of graphene. The carbon atoms are held together by covalent bonds. Graphite occurs naturally and is the most stable form of carbon under normal conditions. It's used in pencils, lubricants, polishes, brushes for electric motors, and cores of nuclear reactors. 
A fullerene is an allotrope (different structural form), of carbon in the form of a hollow sphere, ellipsoid, tube, or one of many other shapes and sizes. The carbon atoms, in rings of 5, 6 or 7, are held together by covalent bonds. Pictured at the left is buckminsterfullerene. 
Diamond is a colourless, transparent, crystalline solid with the carbon atoms arranged in a crystal structure where each carbon atom is covalently bonded to four adjacent carbon atoms located at the corners of a tetrahedron. Diamond is the hardest known material. At room temperature, diamonds do not react with any chemical reagents including strong acids and bases. Diamonds are extremely rare; most come from the Earth's mantle.
Carbon is unique among the elements in its ability to form strongly bonded chains, sealed off by hydrogen atoms. These hydrocarbons are extracted naturally as fossil fuels (coal, oil and natural gas). Some are used as petrochemical industry products such as polymers, fibres, paints, solvents and plastics. Impure carbon in the form of charcoal (from wood) and coke (from coal) is used in metal smelting. It is particularly important in the iron and steel industries. Carbon fibre has many uses as a very strong, lightweight, material. It is currently used in tennis rackets, skis, fishing rods, rockets and airplanes. A more recent discovery of carbon nanotubes, as well as fullerenes and atom-thin sheets of graphene, has revolutionised hardware developments in the electronics industry and in nanotechnology generally. Living things get almost all their carbon from carbon dioxide, either from the atmosphere or dissolved in water. Photosynthesis by green plants and photosynthetic plankton uses energy from the Sun to split water into oxygen and hydrogen. The oxygen is released to the atmosphere and bodies of water, and the hydrogen joins with carbon dioxide to produce carbohydrates. While the total amount of carbon on earth does not change, the element is endlessly circulated between land, sea and sky. This carbon cycle, along with similar cycles of water and nitrogen, is a key part of the reason why life is sustained on earth. Plants and animals absorb or eat carbon, releasing it again when they die. Sometimes this carbon makes its way into the atmosphere and sometimes it accumulates on earth, in sedimentary rocks or fossil deposits, for example, or is dissolved in the ocean. From there it is eventually again recycled via erosion, sedimentation, and the burning of fossil fuels, which transfers carbon that was once contained in living creatures and plants into the atmosphere. This latter activity is now disrupting the natural carbon cycle. Climate Change 150 years ago the natural concentration of carbon dioxide in the Earth’s atmosphere was 280 ppm. In 2013, as a result of burning fossil fuels with oxygen, the level had reached 390 ppm. Currently (2024) the level is 420 ppm. Atmospheric carbon dioxide allows visible light in but prevents some infrared escaping. This is called the 'greenhouse effect'. It keeps the Earth warm enough to sustain life. However, an enhanced greenhouse effect is underway, due to a human-induced rise in atmospheric carbon dioxide. This is affecting living things as our climate changes. |