>>25492251
The problem with a deep biosphere is that it is very slow. Bacteria kilometers beneath the ocean floor are able to survive by developing very slow metabolisms, taking decades, even a century to divide, while in the surficial biosphere where food is plentifully available, bacteria can divide and reproduce in ~20 minutes. Much of the oil and gas is produced by purely abiogenic processes, and these processes are revealed by the existence of Titan's seas of hydrocarbons, that were certainly only produced by abiogenic processes.