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Re: Impact only a part of it all....



John M. Dollan wrote:

> Not to rehash a subject that, I am sure, has been debated to death, but
> I am curious about one thing.
>
> Why does everyone (meaning the public, of course, but also the people
> who tend to support this theory) believe that the KT impact was the sole
> cause of Dinosaur extinction?

A lot of reasons.  First, it's definitely a very attractive idea. 
People like the idea of big, hulking creatures getting wiped out by a
bolt from the blue.  Second, it does explain the direct physical
evidence, better than any other _simple_ hypothesis yet advanced.  Also,
Louis Alvarez is a rather strong-willed man, and more or less shouted
down a lot of his opponents.  (There are also a few ugly rumors of
papers arguing against the impact theory being censored by major
journals, but rumors only, no more.)

There's also a desire to believe that the K-T extinction is somehow
unusual, and must have had an unusual cause.  It isn't; it's merely a
statistical outlier on a curve of mass extinctions of many sizes.  It
isn't even the largest mass extinction known -- that honor goes to the
terminal Permian event, which as far as anyone can tell had entirely
terrestrial causes.

Food for thought: A detailed study of nondinosaurs in the Hell Creek
(Cretaceous) and Tullock (Tertiary) formations of Montana showed that
slightly less than half of nondinosaurian vertebrates, from fish to
crocodilians, survived the extinction.  Some groups were heavily
affected, others only lightly, and at least one group, the champsosaurs,
actually _increased_ in numbers and diversity.  The most common group in
the study, turtles, seems to have taken almost no notice of the
extinction: of eighteen species present in the Hell Creek, sixteen also
appear in the Tullock.  This study is published under the lengthy title
"Non-Dinosaurian Lower Vertebrates Across the Cretaceous-Tertiary
Boundary in Northeastern Montana"; Laurie J.
Bryant wrote it, and it's available from Amazon.com for something like
ten or twelve dollars.

-- Jon W.