Dear Cecil: We all know that oil came from dinosaurs, or, at least, from the decomposition of organic (i.e., formerly living) materials — hence the term "fossil fuels" and the Sinclair dinosaur. But is it really true? Were there really enough dinosaurs — or even plant life — to create the billions and billions of gallons of known oil reserves? What is the physical process that converts dead reptiles and/or ferns into a homogeneous carbon compound that bears little resemblance to the molecular structure of plants and animals? ("Heat and extreme pressure" seems a little vague — and anyway, I thought that produced diamonds, not oil.) Has the process been duplicated in the laboratory? Isn't the source of oil more likely to be natural geologic processes? Larry Orr, via e-mail

Cecil replies:

Forgive me for hitting the energy questions pretty hard lately, but every trip to the gas pump these days brings the subject painfully to mind. Evidently you’ve forgotten my 1986 adumbration of “abiogenic” oil, which focused on the work of the scientific maverick Thomas Gold. (See The Straight Dope: How many dinosaurs did it take to make a barrel of oil? ) Like you, Gold doubted the conventional wisdom that petroleum derived from plant and animal remains. Instead he thought it welled up from inorganic sources deep within the earth, the implication being that there was a lot more down there waiting to be found than most experts thought. With that in mind, Gold persuaded oil prospectors in Sweden to bore an ultradeep hole in that country’s Siljan Ring, the site of an ancient meteorite strike that had cracked the earth’s crust. Gold hoped to find primordial petroleum seeping up through the fissures, far below the level at which oil is normally found — proof of his theory.

We’ll get to the results of that little treasure hunt in a second. But first let’s look at this skeptically: what makes mainstream geologists so all-fired sure that petroleum is of biological origin? The idea seems bizarrely complicated on first encounter. Contrary to wide belief that dinosaurs were centrally involved, oil is thought to have derived mainly from single-celled plankton that flourished tens to hundreds of millions of years ago in nutrient-rich environments, such as lakes and the shallow seas above continental shelves. Upon their demise, the plankton sank to the bottom and were buried in sediment before their remains, rich in hydrocarbons, could decompose. Chemical and biological processes then converted the plankton bits into a waxy substance called kerogen, some of which over time was forced down deep enough that its temperature rose to between 65 and 150 degrees Celsius. This was the “oil window” — the range of conditions under which slow roasting and a bit of catalytic basting could rearrange the organic ingredients into crude oil. (The heat and pressure needed to create diamonds, since you asked, are much higher.) The petroleum then migrated by complex means to reservoirs where it was sheltered until humans could pump it out. I personally don’t doubt this scenario, but you can see where the idea that it would produce two to four trillion barrels of commercial-grade crude might move some to think: Get out.

Fact is, the bio- and abiogenic theories — let’s call them B-oil and A-oil — competed for quite a while. According to geologist J.F. Kenney, an A-oil advocate, B-oil was first proposed by a Russian scholar in 1757, while A-oil was advanced by western Europeans a half-century later. In one of those quirks of history, the compatriots of the original geniuses then switched sides. Russian chemist Dmitry Mendeleyev, the guy who worked out the periodic table, came out strongly for A-oil, a view held by Russian and Ukrainian geologists to this day. Meanwhile, pretty much everybody else in the world bought into B-oil, although important details weren’t worked out till after World War II.

I won’t rehash the A-oil vs. B-oil arguments other than to say that (a) oil can be produced in the lab using both processes; (b) each side agrees that in nature some oil is produced the other side’s way; and (c) circumstantial evidence strongly favors a B origin for almost all found to date. That hasn’t deterred the A team, though, which brings us back to the Siljan Ring. The 6.7-kilometer borehole completed in 1990 didn’t come up a gusher but did recover 15 tons of oily sludge. When the B-oil crowd objected that it was just drill lubricant, the Swedes dug another hole using a water-lubed drill and again struck sludge. Eh, it’s probably B-oil that migrated from elsewhere, said scoffers. In short, nothing got settled. Professor Gold having gone the way of the plankton in 2004, a few other Western scientists have taken up the A-oil cause, although foes far outnumber fans.

Does it matter? Absolyutnyi, say the Russians. They claim they’ve found oil in supposedly non-oil-bearing rock, that there’s lots more where that came from, and that they’re going to try like hell to find it. No doubt when we scoffers get desperate enough, so will we.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.