If you take an average soil sample, it contains lots of organic matter, unless it is completely mineral like desert sand. Oganic matter always has C, H, O elements, and often N. Peat bogs for example, are classed as a type of soil and can contain almost only organic matter, with many kilos of carbon per cubic meter, rainforest soils are sometimes meters of peat, it can catch fire. soil can't. Humus, in forest soils are also mostly organic. If carbon fixing life is removed from a carbon rich land, soil carbon will often slowly return to a mineral state, often as a function of temperature (hot soil mineralizes faster) carbon products get turned into simpler more volatile lower energy compounds, by being eaten by biota and respired as CO2.

If you take an average soil sample, it contains lots of organic matter, unless it is completely mineral like desert sand. Oganic matter always has C, H, O elements, and often N. Peat bogs for example, are classed as a type of soil and can contain almost only organic matter, with many kilos of carbon per cubic meter, rainforest soils are sometimes meters of peat, it can catch fire due to carbon content. Humus in forest soils is also mostly organic. If carbon fixing life is removed from a carbon rich land, soil carbon will often slowly return to a mineral state, often as a function of temperature (hot soil mineralizes faster) carbon products get turned into simpler more volatile lower energy compounds, by being eaten by biota and respired as CO2.