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Re: Theories on the extinction of dinosaurs



>>Your scenario may have a couple of problems with timing and direction of rate 
>>of
change.  The Deccan traps appear to have been several million years older than 
the
impact (reminds me of Dr. Asimov's thiotimoline), and the amber studies appear 
to
indicate that at the end of the Cretaceous, the oxygen content of the somewhat
more dense atmosphere was about 25%, which is about 25% higher than now, that it
was already falling toward the present level, and had been doing so for some
time.  At the end of the Carboniferous (sp?), the oxygen content had been about
33% (which is about the level at which the biomass could be expected to
spontaneously combust), which then declined precipitously to a low of about 15%
before climbing back up to the high 20's again.<<

That makes sence, if the lighter elements are constantly seeping into space.  
It's
kind of scarey, though.  Perhaps life will go extinct on Earth, not because the 
sun
explodes, but because all our atmosphere boils away and we're left with Mars's 
air.
That would be unpleasent.  :)

>>Rather than saying that it is
accepted that this alone is not enough to fully  account for the complete
extinction of all the life that was extinguished at the end of the Cretaceous, 
I'd
say it was a miracle that anything survived.<<

Mmm, Actualy, the Permain Extinction was much, much worse, and I don't think 
asteriod
impact is a big theory for that one.  Some issue of Discover said something 
about a
massive increase in carbon dioxide in the sea that killed off a bunch of 
plankton.
The lack of plancton killed off most marine life, the lack of which altered
ocean-albedo and screwed up global climate patterns.  Asteriods (inless they're 
really
big) don't do half as much damage as those subtle, chemical changes.  I bet 
that even
if an asteriod the size of the Moon hit us (knocking a good chunk of the 
Earth's crust
into orbit) there would still be bacteria after it was all over.  Those things 
are
hardy.

Dan