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Re: Extinction



 From: VanKathy@aol.com
 > For some theories the time comes where the theory
 > becomes accepted as fact.  The impact theory is one that rightly belongs in
 > this class.

Yes and no.

That an impact *occurred* at that time is virtually certain.

That the impact *contributed* to the extinctions is highly likely.

That the impact was *the* primary cause of the extinctions is
NOT yet adequately established.  It is not even established that
such an impact is theoretically *sufficient*.
 > 
 > The facts are overwhelming:  The famous iridium layer was found at the KT
 > boundary in many locations all over the world and this iridium layer could
 > only have been produced by either an impact or massive vulcanism;

And there *was* massive volcanism.  The formation of the Deccan
Traps in India spans the K-T boundary.  Dionsaurs are known right
up to the beginning of the magma floods, and some dinosaur bits
are even known from pauses in the volcanic activity.  Yet when
the activity stopped there were no more dinosaurs!

Is this a coincidence?  Maybe, but maybe not.  If this is a
coincidence, why is not not possible that the impact is also?

Note, there is no real reason to suppose the Deccan volcanism
produced the iridium spike - that does seem to be due to the
impact.

 > Ash has
 > been found in the KT boundary in many locations indicating massive fires
 > which is consistent only with the two reasons above; Evidence of an
 > unbelievably huge tsunami have been found radiating from Mexico thousands of
 > miles away containing shocked quartz from a massive impact; And, of course,
 > the gargantuan 120 mile crater was found surrounding the Yucatan in Mexico.

Yep, all of this is evidence that the impact *occurred*.

NONE of this is evidence that the impact *caused* the extinctions.

That requires a different class of evidence.  A type that is harder
to get - high precision timing evidence.

There is also the fact that the impact coincided with a major
volcanic episode.  The evidence for the timing of this is, if
anything, even more thoroughly established than that of the impact.

There are also some good pieces of *fossil* evidence that the
diversity of dinosaurs was down well prior to the impact.  Some
reduction of diversity is noted as much as 3 million years prior,
at the beginning of the Late Maastrichtian.

 > So they say that their old theories are still really correct and that
 > the dinosaurs would have died off anyway if the impact had not occurred and
 > simply hastened their demise.  Well, doesn't this sound a just a little too
 > coincidental?

What I would say is that the extinctions would have been less severe
without the impact, but would still have been present.  Thus it
is likely that some dinosaurs would have survived without it, but
the result would probably have been a major faunal reorganization
similar to that which happened at the Jurasic-Cretaceous boundary.

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

The peace of God be with you.