Pyrolithotrophs

The science of deep earth biology has taken off in recent years. There are entire ecosystems which do not depend on the sun for energy - examples include the famous chemolithotrophic thermal vent bacteria, which use for energy the sulfur compounds emitted as well as the recently discovered bacteria which react water and basalt for energy. Basically any chemical reaction which can occur in a living cell has been harnessed by some species of bacterium to provide energy.

Bacteria have been very good at exploiting energy sources. I theorize that there must be bacteria in the deep earth which use heat differentials to generate energy. Microenvironments with large, stable heat differentials are probably very common in the deep earth, where cooler fluids moving downwards encounter warmer rocks heated from below. One can imagine that a biofilm on a warm rock with cool fluid moving by could run endothermic reactions on this differential, using the heat to catalyze an energy producing reaction (generation of ATP), then regenerating the components of this reaction on the cool side.

These organisms would be difficult to isolate. Common culture techniques do not create temperature differentials of this sort, and so these organisms could not grow. PCR experiments on soil have demonstrated that many more species exist in the soil than can be cultured - the demonstration that unique ribosomes can be found does not tell you much about the organism, though.

One way to track these things down and create a culture environment to grow them might be a deduce what sort of reaction they might use to harness heat energy. A clue is the presence of huge stores of liquid oil. The origin of oil is still controversial - possibly it is actively generated by deep earth ecosystems. My knowledge of organic/inorganic chemistry is too limited to propose specific reactions - the likely candidate would be an endothermic reaction which generates long chain alkanes as a final product (as our metabolism generates CO2 + H20).

One might ask - who cares if there are pyrolithotrophs? For one, the possibility of huge, unknown ecosystems in the earth is (to me) as exciting as the existence of unknown ecosystems on other planets. For two, an awareness of the various forms life might take is necessary if we are to identify life on other planets - which might be very different than it is here. For three, if our oil is being actively generated by a live ecosystems, it would be prudent to understand and protect it at least - and possibly even cultivate it!