Fossil Fools?

Is it true, dear polymaths, that oil and natural gas are synthesized abiotically? They haven’t anything to do with “fossils”? They’re being formed all the time from carbon in the earth’s mantle?
If that’s true why does everybody still call ‘em “fossil fuels”, other than the lure of alliteration?


Because hydrocarbons are found on other bodies in the solar system and in interplanetary and interstellar space, there has been speculation that some fraction of the Earth’s reserves of hydrocarbon fuels are generated abiotically. This case was made in Thomas Gold’s 1987 book Power from the Earth. Mainstream (consensus, peer-reviewed funded) researchers have largely discounted these theories, although some of his original speculations on the Deep Hot Biosphere have been largely confirmed by subsequent research.

There is abundant evidence that many hydrocarbon deposits are “fossil fuel” from ancient vegetation. This comes from the strata in which they are found and remnants of the organisms from which they formed found in them. But at this point I’d consider Gold’s argument that some hydrocarbons are abiogenic as “not proven”, although arguing so will get you cancelled in many venues.


Just to add to our host’s excellent reply – whether hydrocarbons are generated biotically or abiotically, either way they normally have to migrate through the subsurface and accumulate in favorable subterranean rock strata in order to be economically recoverable. (Setting aside for now the complication of “shale oil”). What about a century and a half of industry experience has shown is that we can drain those accumulations much faster than they can recharge (if indeed they can recharge at all). In that sense, it hardly matters how the hydrocarbon was generated – it is those locations of accumulation (“reservoirs”) that count.

As a side note, coal is also classified as a fossil fuel. And the existence of fossil vegetation in coal could be considered to be very strong evidence that coal was sourced from biological material. Then to further complicate the situation, methane – a gaseous hydrocarbon – is very commonly found in coal seams, the “firedamp” which has caused many a mine explosion and taken many lives. The close association of coal and hydrocarbon gas might be taken as evidence that at least a significant part of gas accumulations have a biological origin.

The only real peculiarity about this topic is, as Mr. Walker mentioned, the very strong academic resistance to exploring the plausible hypothesis that at least some hydrocarbons were generated abiotically.