Flexi Says: Flowing water can slowly dissolve carbon in sedimentary rock. Most of this carbon ends up in the ocean. The deep ocean can store carbon for thousands of years or more. Sedimentary rock and the ocean are major reservoirs of stored carbon. Carbon is also stored for varying lengths of time in the atmosphere, in living organisms, and as fossil fuel deposits. Fossil fuel stores the very small portion of total carbon on earth that is around 0.006% only. The total carbon potential of the Earth’s known fossil fuel reserves contributes to around 3000 gigatonnes CO2.