The majority of carbon transfer from plants and animals to the soil primarily occurs through the decay of dead organisms. When plants and animals die, decomposers such as bacteria and fungi break down their bodies. This process releases carbon atoms back into the soil in the form of organic matter and nutrients, as well as carbon dioxide through respiration.
Therefore, the most accurate statement would be:
The decay of dead organisms releases some carbon atoms from their bodies into the soil.
This emphasizes the role of decomposition in transferring carbon back into the soil ecosystem.