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Re: patterns in extinction, etc.



From: PWSPARKS@aol.com

 >  I think that looking at the need for an unlikely conmbination of
 > factors to explain one extinction event may be the wrong way to go.

Of course.  That is why I compared the K-T extinctions to the Permo-
Triassic extinctions.

Regressions, cooling, flood volcanism, and relatively anoxic oceans
are each associated with several different extinction peaks (including
some lesser mass extinctions of less extent than the Big 5).

Three of these occur in connection with the K-T extinction.

 > There have been 5 very major snuffs and a bunch of other less
 > encompossing events and if it takes a very complicated series of
 > events to cause each one their likelihood would be very very rare.

I would not say a "complex" series of event, merely the close
co-occurance of several different processes that cause population
stress.  Note, I am not even saying a *particular* combination
is required.  Any similar combination of stressing events would do.
Thus the Turonian extinction is associated with an Ocean Anoxic Event,
the K-T extinction is not.

And mass extinctions ARE rare! So the probabilities need not be
very high.

 > I'm not saying that there were not a combination of things, but this
 > combination should have some likelihood of occuring at the same
 > time, maybe one casues the other.

Remember, since I am not talking about a *specific* set of factors
that must always be present, the probability to be calculated is that
of *any* sufficient co-occurance, not the probability of the specific
co-occurance that happened to cause the K-T extinctions.

 > If this is a necessary part of the extinction process then one would
 > expect it to happen at each of the major events or at least what it
 > caused should have happened.

In this theory *nothing* is a *necessary* part of a mass extinction.
Also, in this theory no *single* factor is a sufficient cause for
a mass extinction.

For *some* mass extinctions *one* of the contributing causes may have
been an impact.  For others there was no impact - some other factor
took its place (perhaps the glaciations for the Permo-Triassic one,
for instance, or an OAE for the Late Triassic extinction).

 > What I'm really trying to say is that it is very improbable that
 > each event was caused by a different series of locked in
 > causes. Either one thing can bring it off or the same series of
 > things must have some distinct probability of happening at the same
 > time.

Or a slightly different set of causes produced each individual
extinction, the only common factor being that all of them had several
causes.

Note, this is not just MY idea.  Dr. Archibald also supports this idea,
as do several other paleontologists.

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

The peace of God be with you.