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October 27, 2007 12:15 AM   Subscribe

The oil we use today was made from a biomass from a certain era. When was it, and how long was that era?

Please tell me me when oil was made. (For example) from living things that grew 1.3 quajillion years ago to 0.9 quajillion years ago--or whatever. I want to know when it was, and how long that period was.

Mostly I'm looking for a span of time.
posted by sourwookie to Science & Nature (7 answers total) 2 users marked this as a favorite
The term for it is "Carboniferous". It extended from 359 to 299 million years ago, plus or minus.
posted by Steven C. Den Beste at 12:18 AM on October 27, 2007

A lot of "oil" is available in "tar sands" which are felt to be much younger than the era Steven C. Den Beste has linked.
posted by paulsc at 12:33 AM on October 27, 2007

The theory that PaulSC links to is far from universally supported among geologists.
posted by Steven C. Den Beste at 12:43 AM on October 27, 2007

Just to be contrarian, I'll mention that Thomas Gold hypothesized about non-biological origins of oil in his 1999 book, The Deep, Hot Biosphere. It appears, from Wikipedia, that there's not much support for abiogenic theory, but I'm no geologist, and it's making my eyes glaze over. I seem to recall enjoying Gold's book much more. YMMV.

(on preview, this is what paulsc is talking about, albeit via different links)
posted by mumkin at 12:51 AM on October 27, 2007

There is a problem with that theory. 1.1% of naturally occurring carbon is isotope 13, which is stable. Photosynthesis preferentially selects carbon-12 over carbon-13, so organic carbon has a lower ratio of C-13 than inorganic carbon. (They're chemically identical, but the mass difference is significant.)

I remember hearing that petroleum has the same C-13/C-12 ratio as organic carbon, but one time I tried googling for a reference and couldn't turn up any. (If you search for anything relating to isotope 13, you turn up thousands of hits relating to MRI, for some reason. What I wanted was probably buried in there somewhere, but I never figured out how to find it.)
posted by Steven C. Den Beste at 1:00 AM on October 27, 2007

It varies greatly depending on the deposit that's being drilled. Steven C. mentions the Carboniferous, but a lot of the production in the Gulf of Mexico (for instance) comes from the much younger Jurassic and Triassic.

It's not as though there was some magic era in the past when everything came together just right and all the conditions were met to form an oil deposit that appears in one single layer everywhere in the world. Instead, it really depends on where in the world the oil is coming from.
posted by adiabat at 1:36 AM on October 27, 2007

Here's an abstract that discusses what I think Steven C. Den Beste is referring to in terms of carbon ratios.

But I am thinking about this question as a geologist and not as a biologist, which I suppose complicates things somewhat since oil can migrate to shallower depths. That is, just because the oil is trapped in a Jurassic deposit doesn't always mean the biomass that formed that oil is from the Jurassic. Even with that caveat, I stand by my previous answer: It depends.
posted by adiabat at 1:44 AM on October 27, 2007 [1 favorite]

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