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Re: Extinction

>From: VanKathy@aol.com
 > Sir, you seem to have missed my point entirely.  I am suggesting that the
 > date of the Chixculub impact can be dated directly from the fossil record at
 > any place on the globe.  An impact creating a 120 mile crater would devastate
 > life everywhere on earth, and if it were to occur 8 million years prior to
 > the KT boundary, as you pose as a possibility, a mass extinction would have
 > occurred there,

That is effectively circular reasoning!  It is *far* from established
that such an impact, by itself, *would* cause such an extinction.
In fact a discovery that the Chixculub impact *had* occured 8
million years prior to the K-T boundary would be prima facie evidence
that such an impact is *not* a sufficient cause for major extinctions.

In fact there are several known moderate sized impacts that *don't*
have associated extinction events, at least not measurable ones.
The issue then becomes whether the extinction rate increases non-
linearly with impact size or not.  While this is quite reasonable,
it is not yet adequately demonstrated.  It is also quite possible
that the extinction rate increases linearly, in which case the
Yucatan impact would *not* have been sufficient in itself to cause
the extinctions.

At present there are effectivly *two* research issue of concern:
        1. where was the K-T boundary impact.
        2. was the impact *by* *itself* the primary cause
           of the extinctions.

What Dr. Holz was pointing out is that even #1 is not yet clearly
answered - there are indications that Chixculub may *not* be the
boundary impact.  Even the tsuname deposits are not, in themselves
sufficient evidence of this.

And #2 is still largely unaddressed, IMHO.  Most of the research
up until now has concentrated on deomnstrating the *existance*
of the impact.

Also, to maintain #2 you must assert that the Deccan volcanism
was a coincidence, while at the same time denying that the imapact
could be a coincidence.

 > but as you probably know T rex and others not only flourished
 > during this time period but actually evolved. 

Actually, T. rex had not yet evolved 8 million years prior to
the K-T boundary.  That was the time of Albertosaurus and
 > Futhermore, I do not claim that the Mexican impact was the sole impact -- I
 > expect the object fragmented from tidal forces in a fashion similar to the
 > recent comet strike of Jupiter -- but I do believe, as I feel is obvious,
 > that the object that generated the Chixculub crater and any sister impacts
 > exterminated the dinosaurs.

Such a break up would only have occured if the object were a comet.
Asteroids are much more solid, and would tend to remain intact.

And if the impacter were a comet, it is not clear it would have
produced a large crater. There is some reason to suspect that
comets tend to break up high in the atmosphere.  First, there
was the Tsunga explosion a few decades ago, and second there is
the evidence that the Shoemaker-Levy fragments broke up quite
high in Jupiter's atmosphere (though this is still not a settled
issue - the data is still bein analyzed).

[The Tsungas event produced no crater at all].

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.