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Re: Extinction scenarios



Jeff Hecht wrote:
<<As Allen said, it's more realistic to think of the crater left behind -- a
hole the size of Connecticut, roughly (by my calculations) 1.4% of the
Earth's diameter. It landed in anhydrite, ejecting large amounts of sulfate
as well as CO2, stuff that didn't do the atmosphere any good.>
and:
<You're right in saying that the chain of events from impact to extinctions
is not well documented. But there are many possibilities. Perhaps we
haven't fully appreciated just how much a big dose of sulfuric acid (which
the surfates become in moist air) can devastate the global ecosystem. Or
perhaps we're missing something terribly obvious. >
   Perhaps not obvious, but you're on to something, as far as I'm concerned.
The volatiles and ejecta from impacts can be of spectacular importance.  Take
the impacts of Shoemaker-Levy on Jupiter. Each fragment of S-L was much
smaller than the K-T object, and yet one fragment (I think it was G) punched a
hole in Jupiter's atmosphere LARGER THAN THE ENTIRE EARTH, with a secondary
fallout ring that was much larger than the diameter of the Earth.  Much of
this action was due to the fireballs that Hubble and Galileo observed so well.
Truly immense explosions of gas.
    It seems to me that 65 MYA, the eruption of white hot water vapor (from
the impacted ocean) plus CO2 (from the underlying limestones) would have
represented a detonation of global-sized proportions.  I think someone writing
about S-L's impact made this point, almost offhand, in an article in
Astronomy, but no one, to my knowledge, has really run down the possibilities
for destruction by the shock wave itself.  As I recall, the writer pointed out
that the hypersonic expansion of gasses would create a massive pressure wave
capable of propagating for great distances (going fastest and farthest in the
denser atmosphere at sea level).  As elementary physics class tried to teach
us, if you compress a gas, without adding heat, it will still heat up, due to
the increased rate of molecular collisions when density is increased.  Thus, a
propagaing pressure wave will heat the atmosphere as it passes, then the air
will return to its original temperature after the pressure wave is gone.
    The thing is (and I just MIGHT be the first to state this) the unfortunate
coincidence of a large bolide hitting a shallow sea over deep carbonate rocks
might have created an impact unique in the magnitude of its shock wave.
Undoubtedly, the shock wave would be strong enough near the impact to create
the white-hot flash that Alvarez and others have mentioned, but it seems to me
that the PROPAGATING SHOCK WAVE, if big enough, would have also heated air to
white-hot temperatures.  The question is: over how great a distance could this
wave carry lethal heat?  My personal bias is: ALL THE WAY 'ROUND THE WORLD.
    Thus, you might be a Muttaburrasaurus quietly sipping at a watering hole
in Australia, far from the impact, when the first thing you noticed was that
you were hurtling through the air amid white heat.  This of course, would be
your closing observation on conditions in the Late Cretaceous.
    Tom Hopp