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Re: Isotopic Evidence for the K - T Impactor and Its Type

At 09:07 PM 11/12/98 -0500, Michael Teuton wrote:
>Stanley makes the necessary point that one cannot prove the impact caused
>the extinction of the dinosaurs.  I would like to know how this could ever
>be proved.

It could, however, be shown to be the most likely scenario.  This would
require careful analysis of the timing of the extinctions, taking
statistical artifacts into account, and careful analysis of other impact
sites to show they differ in magnitude or type.
>However, the magnitude of this strike cannot be underestimated.  The
>crater's size and shape as well as debris is reasonably clear cut evidence
>of the size of the comet and therefore the amount of energy released.  This
>has to lead to some reasonable estimation of the damages.  A comet striking
>at the necessary angle to create the crater would release enough energy to
>have global impact.  It is unreasonable to argue against this (and I know
>you aren't Stanley).
Global impact is not necessarily the same as causing extinctions.  As the
Mt. St. Helens explosion showed, there are often sheltered locations even
within the core blast area where life survives.  (Not, of course, in the
zone of cavitation and crater formation, but certainly elsewhere).  This
means that even a blast of such magnitude, much could survive.

This is why the effects of *other* giant impacts in the fossil record are
of importance.  If we find another crater of similar magnitude elsewhere,
and it is NOT associated with a significant extinction event, the
considerable doubt is thrown on the whole single-cause scenario.  And I
have certainly heard suggestions that at least one mid-Cenozoic crater is
known of comparable magnitude.

>Whether it caused, hastened or even contributed to the dinosaurs demise is
>conjecture.  However, it is not unreasonable to think it played a role.  (I
>personally think it created havoc, but what do I know).
Actually, my current model is that it was indeed *contributory* to the
extinctions.  This is why I carefully used such phrases as "single cause".

>What is the latest paleobotanical changes before, during and after the

Well, in the Dakotas, there is considerable evidence of ecological impact,
in the form of a post-impact increase in "weedy" species, especially ferns.
 However, this is far from a global effect, as far as I know.

May the peace of God be with you.         sarima@ix.netcom.com