The Oil Drum

I remember reading somewhere that the current rate of oil generation in source rocks, worldwide, was estimated at between a few million and a few tens of million barrels per year (that's per year, not per day). Most of it migrates to surface and is oxidized in the atmosphere - only a small fraction is ever trapped.

The same article estimated that once oil finds its way into a reservoir it has a survival half-life of approximately 100 million years. It will be destroyed when the reservoir is breached (by faulting or uplift/erosion) or buried to a depth where the oil is thermally cracked to methane and graphite. So TK's estimate of "a few hundred million years" sounds reasonable.

Of course the actual source and reservoir rocks can be a lot older. They could have been in place for half of eternity before the onset of oil generation, which depends on stuff like rifting, subsidence/burial and relative movement of mantle thermal plumes (hotspots) and tectonic plates.

I'd like to post a link so I've been scouring the web for the source article, but it's gone beyond recall. Something to do with AAPG, IIRC. I found lots of other interesting stuff, though :)

However... that estimate has been totally screwed up in the past fingernail-paring of geological time. The culprit is a species of semi-intelligent primate that has evolved the ability to short-circuit this important part of the planetary carbon cycle, throwing the chemistry of the atmosphere seriously out of balance.

The immediate consequences, for the primates and the planet, are far from clear. In the long term, well, species come and go and the planet will probably fix itself in less than one Galactic Great Year. So no real harm done, thank goodness.

The novel "Galapagos" (Kurt Vonnegut RIP) suggests that the primates' large brains are an unsustainable mutation that will die out when the primates destroy their own habitat, as usually happens with virulently invasive species.