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Re: Hell Creek (long)



On Fri, 31 May 2002 11:16:58  
 MariusRomanus wrote:
>In the "little" I apparently know.... What I see is that there is indeed 
>evidence for an extintion/impact correlation..... But I do not see a 
>relationship of extinction/impact causation...... Caution in equating 
>correlation with causation is the message I was trying to send.

Oh, certainly, yes...we must always be careful in correlating the cause of an 
extinction with an impact.  But, we must be equally careful in extrapolating 
data from one isolated site in one part of the globe to "prove" a gradual 
extinction.  That was the point I was trying to make.  You may very well turn 
out to be right.  As you say:

>Only time will tell.

>Apparently, some are pretty damn sure of themselves when it comes to an 
>extinction/impact correlation and causation.... I, on the other hand, rather 
>like something that Planetary Physicist Kevin Zahnle of NASA's Ames Research 
>Center in Mountain View, California had to say in his "No Darkness at Noon" 
>article:
>
>"Everyone has their own favorite mechanism. We don't know the facts, so you 
>operate from your intuition."

Well, we definitely do not know all of the facts.  But, we do know some facts.  
We have a crater and a worldwide iridium spike.  So, we are pretty darn sure 
there was an impact :-)  We also have the complete and total extinction of the 
nonavian dinosaurs-a lineage that had survived many smaller "mini-extinctions" 
in the past.  Coupled with the extinction of the dinosaurs was the extinction 
of the mosasaurs, ammonites, many forams, a lot of lizards, amphibians, birds, 
and mammals.  There was something very global going on, both in the oceans and 
on the continents.

Of course, perhaps some of these extinctions were due to more gradual causes 
and others tied directly to the impact.  It is difficult to tell, but I would 
say that most of the current evidence favors a causation correlation between 
the impact and dinosaurian extinction.  Sure, the dinosaurs may have been in a 
brief decline (more data is still needed to confirm this, though), but the fact 
that other such declines had already occurred and dinosaurs survived them 
weakens the hypothesis that any LK stress would have caused extinction without 
the impact.

>Now I am going to respectfully run away from this as fast as I can before I'm 
>told again that something I casually remarked about without ever thinking 
>"Darwin" is a totally out of place misquote of Darwin and that they hate 
>it....

Don't run away.  Perhaps the best aspect of paleontology is that anyone can 
question and hypothesize.  

Steve

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Steve Brusatte-DINO LAND PALEONTOLOGY
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