[muawiyah]

Not my theory. But your answer is directed at a totally different concept ~ namely "primordial oil" ~

I was thinking more of extremophiles having "converted" other, lighter, hydrocarbon sources in the early Earth into munchies for later critters (diatoms, etc.).

This makes the critters with the munchies coincidental with the existence of short chain hydrocarbons, not the primary source.

We also have an incredibly large biomass contained directly in rocks in the crust that, if squeezed out, would undoubtedly deliver something useful to burn.

Now, the question of what you are pointing to, I think it's the idea that quite ordinary bacteria, diatoms, etc. are the final source for fosil oils, with them having cruched it out of hydrogen (from water), and carbon from ?

So, where do they get the carbon?

[Liberal Classic]

Not my theory.

Here's one thing I know ~ other than finding buried reefs, under which heavy hydrocarbons can get trapped, I fail to see where any understanding of biological processes would be needed to find oil.