Carbon can be found in a variety of natural reservoirs on Earth and beyond:
- Earth's crust and rocks: The vast majority of Earth's carbon-over 99%-is stored in rocks and sediments, especially in carbonate rocks like limestone, dolomite, and marble formed from marine organisms' remains
. Coal, rich in carbon, is also a major mineral carbon source
- Oceans: The ocean holds a large amount of carbon dissolved in water, estimated to be about 36,000 gigatonnes, making it one of the largest carbon reservoirs
- Atmosphere: Carbon is present in the atmosphere primarily as carbon dioxide (CO2), with about 900 gigatonnes of carbon in this form
- Living organisms and soils: Carbon is a fundamental element in all living things and is found in organic matter in soils and biomass. It cycles through the biosphere via processes like photosynthesis and respiration
- Fossil fuels: Coal, oil, and natural gas contain significant carbon reserves formed from ancient organic matter
- Other natural sources: Carbon is also found in methane hydrates under the sea and polar regions, diamonds in kimberlite rocks, and even in cosmic sources such as meteorites and interstellar compounds
In summary, carbon is widely distributed in Earth's geosphere (rocks, sediments), hydrosphere (oceans), atmosphere (CO2), and biosphere (living organisms and soils), as well as in fossil fuel deposits and extraterrestrial materials
