From: Technotranscendence (neptune@mars.superlink.net)
Date: Tue Jun 26 2001 - 17:45:48 MDT
On Saturday, May 12, 2001 9:21 PM John Clark jonkc@worldnet.att.net wrote:
> It wasn't just the dinosaurs, no land species that weighed more than about
40 pounds
> survived, perhaps because small animals are more numerous than big ones so
there
> was a better chance at least two would get lucky.
I agree, though, in general, under many different types of environmental
stresses, the species that reproduces faster (this usually correlates with
being smaller) gets lucky. So, the point you make does not necessary rule
out non-impact explanations.
>>A big asteroid hit would seem to be more egalitarian in its affects,
taking out all
>>major groups
>
> It did.
See below.
>>not specifically targeting nonavian dinosaurs.
>
> It didn't.
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.
>>Archibald points out the myriads effects of sea level changes and how
>> this correlates well with the fossil evidence -- much better than an
impact
>> or massive volcanism.
>
> Then why did more than half of the marine species become extinct too?
Marine regression would, to me, seem to explain marine species becoming
extinct. After all, the sea level changes from across the K/T boundary did
reduce the amount of shallow seas, such as the Pierre Seaway in North
America (roughly where the Plains States of the US are now). This would
also account for the rise of many freshwater species as the marine species,
such as sharks, declined.
> And why did
> it happen in less than a hundred years, perhaps much less? And how did
all those
> Buckeyballs (C60) get made at that time if not by an impact? And what
about the
> excess of iridium, where did that come from is not from space?
Archibald's point is not that an impact did not happen, but that it did not
cause nonavian dinosaur extinction.
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.
Cheers!
Daniel Ust
http://uweb.superlink.net/neptune/
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