Overview of Carbon Reservoirs

Carbon is present in each of the Earth’s spheres and in all known life forms. On Earth, carbon is a fundamental building block of life. The places and forms in which we find carbon are called reservoirs.
Carbon combined with oxygen is carbon dioxide (CO2) which is found:
...in the atmosphere
...dissolved in all bodies of water

Carbon combined with hydrogen creates a hydrocarbon, a historically important source of energy as fossil fuels. Fossil fuels are found in our environment:
...as coal
...as oil
...as natural gas

Carbon forms minerals and is found in the earth:
...as carbonate rock
...as diamonds