Every living thing on earth contains carbon. In its elemental form, carbon exists as diamond, the hardest substance known to man, and as graphite, a material more flexible than rubber and stronger than steel. Prehistoric man knew carbon as charcoal.
Carbon is the sixth most-common element in the universe. Because it is a primary element in living material, it is also in petroleum deposits under the ground. Petroleum provides fuel for automobiles and is a primary ingredient in plastics.
Plants use carbon dioxide from the atmosphere in the process of photosynthesis to produce the carbon compound glucose, which they store in leaves, stems, roots and fruits. Animals eat plant parts and digest them. The digestive process releases the stored glucose, which is absorbed into the blood, providing energy for every cell in the body. In the respiration process, animals release the carbon dioxide as a waste product back into the atmosphere.
As of 2014, there are more than 10 million carbon compounds known to man. Carbon as coal provides 30 percent of the world's energy; however, when petroleum is included, the percentage is much larger. Manufacturers use graphite as a lubricant. Scientists continue researching uses of carbon substances in various areas, including the prevention of HIV and as electrical conductors.