1. Carbon is an essential element that is found in all living things. The main forms of carbon are carbon-12, carbon-13, and carbon-14. 2. Carbon exists in the biosphere in several forms including carbon dioxide, methane, and fossil fuels. It is also found in limestone, diamonds, graphene, and carbon nanotubes. 3. Carbon cycles through the biosphere, atmosphere, oceans, and lithosphere in a process where it is exchanged between living organisms and the environment. This movement of carbon is vital for life on Earth.