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Re: Theories on the extinction of dinosaurs



At 03:54 PM 11/12/99 -0500, TomHopp@aol.com wrote:
>I tend to agree with Jim. The overwhelming factor had to be that huge imact. 
>The issues of Deccan volcanism and oxygen levels have been invoked more as 
>alternatives than as co-variables.

Not by me, nor by such authors as Archibald.  Citation as co-variables is
actually quite well established in the literature.

> For the trapps, the fact that they had 
>been going on for some time before the extinction mitigates against them, but 
>does not rule them out.

Only if one expects the causative factors to be *immediately* effective,
and even then only if the Deccans were the primary or sole cause.  When one
moves to multifactor models, partial contributory factors are *not*
expected to exactly match the timing of the extinctions.  It is the maximal
confluence of the contributory factors that determines the timing of the
extinction peak.

>    After having watched Schoemaker-Levy slam into Jupiter, knocking holes in 
>its atmosphere larger than the diameter of the earth, I'm content that a 
>comet impact could scald the whole surface of the earth with a giant pressure 
>wave.

The impact would not have been directly comparable.  Shoemaker-LEvy had
fallen through a larger gravity potential than would the Yucatan impactor.
This alone would make the S-L impact results larger.

Also, geometric factors (the curvature of the Earth, mountain ranges) would
tend to partially shield portions of the Earth from the direct impact effects.

> This would leave only animals that dwelt under ground or water as 
>survivors -- cave-and burrow dwelling mammals and birds come to mind. Plenty 
>of modern examples of those.
>    So, impact alone could have done it.

OK, now explain the planktonic extinctions in the marine realm.  By this
concept they should have been shielded by being in the water!


The pattern of terminal Cretaceous extinctions is complex, and defies any
simple criterion for determining survival.

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