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Re: Extinction scenarios



Regarding a world-sweeping white hot air pressure wave out of Chixulub, John
Bois wrote:
<are you suggesting that 100% of the 100% survivors in Montana were burrow
dwellers.  I'm not sure where it is from but little purgatorius (putative
ancestor of primates) was almost certainly not a digger and was probably
arboreal (at least from memory).  And I'm uncertain how a heat/shock wave
would work.  Would the white-hotness heat up the air for any extended time
(minutes? hours?).  What is the killing mechanism, burnt flesh, heat
stroke--bearing in mind that most extant burrows are far more shallow and
conductive than the depth of an
hadrosaurs body core. Could a non-avian find protection in a lake? My point
here is that it is much easier to invoke killing mechanisms than explain how
they kill some things and not others.  And are you aware of the diversity of
killing mechanisms attributed to the bolide?>
  First off, let me make the disclaimer that my credentials are marginal in
brooding-came-first evolutionary biology, and more like non-existent in
asteroid impact physics.  However, I appreciate your interest in this concept,
which as I mentioned before, I recall having seen mentioned in passing in an
issue of Astronomy Magazine dealing with the Schoemaker-Levy comet impact on
Jupiter.
    That said, I'd urge you to take a look at file footage of nuclear blasts
that are occasionally trotted out for TV dramatic purposes.  In most, you can
see an initial white flash from the detonation, followed shortly by a shock
wave of air pushed outward by the explosion.  This shows in aerial film as an
expanding circle of atmospheric disturbance, or if viewed from the ground, the
detonation flash followed a few moments later by a sudden outward pressure
blast against buildings, trees, etc., which soon are pulled back toward the
center again as the overpressure is relieved and results in a momentarily
lowered air pressure.  Somewhere in between is the time spent within the
hyperpressurized front of the wave.  This pressure is not white hot in footage
of nuclear blasts, because they are so miniscule compared to the K/T event.
How long would the time of white-hotness last?  I don't know - best ask an
astrobleme specialist or nuclear bomb engineer.  However, it might be long
enough (a second or two) to parboil the skin off your hadrosaur, and to light
up a pretty big conflagration of bushes and trees.
    Regarding survival of non-burrowing mammals in Montana:  Did they survive
in Montana or Asia or Newfoundland?  Any small population could have spread
out to reclaim a devastated world in a geological trice, so how do we really
know ANYTHING survived in Montana?
   Regarding other bolide-extinction mechanisms: I'll go with most of them,
clouds of dust, clouds of ash, runaway greenhouse followed (or proceeded) by
killing cold, poison gasses, incandescent ejecta swarms, and I kinda liked the
one about a ring forming in orbit to shade the equatorial regions.  I just
thought white-hot atmospheric pressure waves hadn't had their due.
    Tom Hopp