Since organic and inorganic forms contain carbon, it's safe to say that the carbon stored in fossil fuels are from the decomposed plants and animals that made the fossil fuels.
Explanation:
Fossil fuels are made from decomposing plants and animal matters. These fuels are found in the Earth's crust and contain carbon and hydrogen (hydrocarbon).
Carbon is stored in the lithosphere in both inorganic and organic forms. Inorganic deposits of carbon in the lithosphere include fossil fuels.
