Oil stories

While there is no truth in the accusation flung by creationists that evolution is a belief and not a fact, it's important that science does not indulge in dogma. I learned something interesting the other day that made me stop and think about that.

Mrs Zen asked me how oil is formed. I said, well, it's made of the crushed bodies of prehistoric sea animals and land plants -- plankton, ferns and the like -- that died and sank to the seabed, and then were covered with mud, which became rock and pressed the animals' remains so hard that they were transformed into oil. I realised as I was saying it that I was doing some handwaving, so I went to look it up.

I was astonished to find that there are competing explanations for the provenance of oil. The first, and most widely held, theory is the biogenic theory of oil's origin. It's more or less as I described to Mrs Z. The animals were crushed into a type of rock, which under pressure from layers of rock on top of it is transformed into oil. The oil seeps through porous sedimentary rock, until it is trapped by harder rock into reservoirs, which we drill into and exploit. (Oil shales and the like are types of rock that have not completely undergone the process.)

However, some geologists, mostly Russians, propose an abiotic theory of oil's origin. (Google "abiotic oil"; add in "Thomas Gold" to narrow your search a little -- Gold popularised the theory.) In their theory, oil is continuously created in the depths of the earth, as rising hydrocarbons are attacked by bacteria. They suggest that the biogenic theory has difficulties explaining why there is oil -- or hydrocarbon precursors of oil -- in deep strata (it should only be in relatively recent rocks; the biogenic supporters say that the same seeping that forms the reservoirs we tap allows the oil to slide down to deeper layers through faults, which is very plausible), why it is found in nonsedimentary rocks (same explanation), why it contains certain impurities that suggest bacterial infection of the kind they suggest (the biogenic side suggests that not all oil has the characteristics the abiotics claim it should have), why are some reservoirs refilling when they are supposed to have been pumped dry (all sorts of explanations, too much to go into here), why do we keep having to revise reserves upwards (biogenic side points out that oil exporters and petrol companies simply lie about reserves), where sufficient animals came from. They note that the chief supporting evidence for biogenic origins is "it looks like the constituents of animals". It doesn't take a genius to point out that things can look like each other without actually being each other. The minus column for the abiotic theory is dominated by oil's containing the unmistakeable signs of the organisms it once composed, along with some problems of magma chemistry that the abiotic theory would struggle to resolve, and the reproducibility of the organic processes that probably made oil.

Like all great scientific questions, this one seems to have a relatively easily solution: if the biogenic theory is correct, there should only be oil where the right conditions pertained at the right time in the past; if the abiotic theory is correct, there should be oil everywhere in the planet in some measure. As a side note, it's of course best that the abiotic theory is right. If it is, we need not fear the end of oil, because there will be lots more. If you are thinking that the growing popularity of the abiotic theory has something to do with peak oil's approaching, well...

Naturally, it's perfectly possible that both answers are right. But probably only one is right, and the correct experiment would exclude the incorrect explanation (which is the scientific way). (Where there was an analysis of hydrocarbons found in deep drilling, the isotopic breakdowns have not matched that of economic natural gas. This is reasonably close to a conclusive disproof. At the very least, abiotic theory supporters would need to find isotopic matches in abiotic hydrocarbons in other deep drills to keep their theory alive.)

Your textbook at school doubtless, like mine, said "oil was formed from prehistoric animals who were crushed". It is the majority view (the enormous majority view) but it is not an eternal truth. It is a comfort that we know that if we did drill holes across the earth's surface and we found oil everywhere, we would abandon the biogenic theory (eventually -- paradigms sometimes only shift gradually). Probably. We'd probably actually adopt both as explanations, because the biogenic theory is so compelling and plausible. (Noting the reasons I give for keeping the biogenic explanation, I remind myself that science deals in explanations, approximations, models that work, and not pronouncements about how things are -- although often it does translate into the latter. It's the very tentativeness of science that religious bigots prey on. They know we won't claim to have eternal truths and they have no qualms in doing so. But on the other hand, it's clear that science, as well as having difficulties in being "right", struggles sometimes to be "wrong". It is, however, useful to remember that many questions in the natural world are not easily settled by single observations but by the accumulation of evidence.)

The other thing I learned is that there is a process to make petroleum from its constituent materials, which Germany used in the second world war, when it could not get hold of any oil (and South Africa uses today). I don't know at what point it would become economic (in other words, when its price per gallon would be lower than the petrol extracted from oil's) or if it ever would (the Germans, having no choice, were willing to spend large on it, but I'm not sure they ever were able to make useable quantities). You don't hear a great deal about it, so presumably it's not viable.

While writing this poast, I happened to find an article on disproofs of the abiotic theory. I like the checklist in particular. Well, widely accepted hypotheses are not always con-jobs.

posted by Dr Zen @ 11:01 am