There are some interesting details to consider regarding the theory that oil on Earth is of biological origin from ancient life.
There are apparently hdrocarbons in considerable quantities on other planets in our solar system (I forget which ones, but I remember reading about it.) It is unlikely that these formed because of life in ancient oceans.
Also, here on Earth does it have to be one or the other? Could it not be both? Could oil not have formed as a result of living one-celled animals in ancient seas, and formed pools that are relatively near the surface? And then again, might it be possible that oil formed deep in the Earth because of non-biological processes, and (get this) maybe in quantities that are far, far greater than anything that formed from biological sources.
Finally, it is interesting to note that Big Oil interests would not be overjoyed to learn that oil is available in untold quantities if we just drill deep enough! This does not make the non-biological deep-oil theory correct. It only means that the Powers that Be might not be wildly interested in pursuing it, though. I am not suggesting a conspiracy theory here, just saying that some people who are very rich and powerful and have a lot of control over a lot of things might not be enthusiatic about deep-oil research.
This might perhaps be true for highly profitable oil companies from major oil-exporting countries, but there are other players in the market. Currently oil-importing countries and oil-consuming industries would have a strong interest in access to unlimited oil. Even if the oil industry is a popular target for conspiracy theories, don’t underestimate the power of these interests either. Also, don’t forget socialist economies, past and present, where such a conspiracy wouldn’t work exactly the same way.
Methane, the simplest hydrocarbon, has been detected in several places in the solar system. Getting the more complex hydrocarbons in quantity, though (or least bigger than ethane in more than trace amounts), may require an environment with a lot of chemical give-and-take, i.e. life.
Hydrocarbons /= crude oil. No-one’s saying all hydrocarbons came from life in ancient oceans. Just because, say, methane (NH4, IIRC) formed on Titan doesn’t mean the array of organic molecules found in oil desposits could be.
Semi-related, Isaac Asimov wrote an essay called The Thalassogens, i.e liquids that serve as the medium for the devlopment of life. He listed off a bunch of candidates and concuded that only three were feasible: water, methane and ammonia. Of these, only water was practical on Earth-like planets
I suppose conceivably, there could be an ocean of methane on Neptune at 100[sup]o[/sup] Kelvin, and if proto-microbes were swimming around in it, trading chemicals back and forth, there might be a gradual accumulation of more complex hydrocarbons. Ethane and propane would still be a liquid at that temperature, but butane wouldn’t.
