In its diamond allotrope, carbon is the hardest known substance in nature.It also has the highest thermal conductivity of any element. Graphite, on the other hand, is one of the softest materials and is black-gray in color. Amorphous carbon is generally black and is used to describe coal and soot.He first noted that the cells of all living things contain atoms taken in from the organism's environment, including carbon; all organic compounds contain carbon.Most carbon consists of the isotopes carbon 12 and carbon 13, which are very stable.One of the key characteristics of carbon is its ability to make long chains of molecules through linking up with other carbon atoms. It is a major element in many rock formations such as limestone and marble.Carbon also has the highest melting point of all the elements. It is found in its allotropic forms of diamond, graphite, and amorphous carbon throughout the world. Carbon is used in some way in most every industry in the world.A very small percentage of carbon, however, consists of the isotope carbon 14, or radiocarbon, which is unstable.
Since this rate is slow relative to the movement of carbon through food chains (from plants to animals to bacteria) all carbon in biomass at earth's surface contains atmospheric levels of C is present at atmospheric levels, the molecule must derive from a recent plant product.The pathway from the plant to the molecule may have been indirect or lengthy, involving multiple physical, chemical, and biological processes.Levels of C can represent either mixtures of modern and dead carbon or carbon that was fixed from the atmosphere less than 50,000 years ago.Because atmospheric carbon 14 arises at about the same rate that the atom decays, Earth's levels of carbon 14 have remained fairly constant.Once an organism is dead, however, no new carbon is actively absorbed by its tissues, and its carbon 14 gradually decays.