From: John Clark (jonkc@worldnet.att.net)
Date: Wed Jun 27 2001 - 09:48:55 MDT
Technotranscendence <neptune@mars.superlink.net> Wrote:
>A big asteroid hit would seem to be more egalitarian in its affects,
> taking out all major groups [...]The survival patterns of different
>vertebrate groups, according Archibald in > _Dinosaur Extinction
>and the End of an Era_, shows a bias toward nonavian > dinosaurs.
>In fact, of 12 groups he gives in a chart on page 126, most -- > 7 --
>had species survival rates above 50%. Two dinosaur groups -- excepting
>birds -- show 100% extinction rates as do Elasmobranchii -- a group which
>includes sharks. Only two other groups -- Metatharians and Squamates --
>show less than 50% species survival rates.
I'll bet if you looked more closely at these animal groups you would find a simple
pattern, the greater the body weight of the adult the more likely it went extinct, and
that's not inconsistent with impact. I'll bet you'd also find a geographical pattern,
the closer the natural habitat of the animal was to North America the more likely it
went extinct. The Chixulub explosion was not symmetrical because the object did
not hit the ground at a 90 degree angle, it was more like 10 degrees and it came
from the south, so North America got a disproportionate share of the blast and the
rain of debris. I believe that's probably why the extinction rate was higher in
North America than any other continent. If you're big or even medium size and live
in North America you're toast, if you're very small and live far from North America
you have a chance.
>Archibald's point is not that an impact did not happen, but that it did not
>cause nonavian dinosaur extinction.
An impact of Chixulub's size only happens about every 100 million years or so,
the idea that it was pure coincidence that a great extinction coincided with
this very rare impact is very hard to swallow. You see a man struck by lightning
and rush over to him and find he is dead. What killed him? Well maybe he died
of a heart attack a tenth of a second before the bolt hit him, but I doubt it.
> For the record, I'm not saying an impact didn't do in the dinosaurs, just
> that there are some arguments which are not exactly unpersuasive to question
> the impact theory.
There are always unanswered questions but it would be misleading to suggest there
is some huge controversy over this. I think in 2001 the consensus in the scientific
community is nearly as strong as it ever gets for anything that an impact caused
the extinction.
John K Clark jonkc@att.net
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