Re: Extinction

[VanKathy@aol.com]

Sarima writes: 

>That is effectively circular reasoning!  It is *far* from established
>that such an impact, by itself, *would* cause such an extinction.
>In fact a discovery that the Chixculub impact *had* occured 8
>million years prior to the K-T boundary would be prima facie evidence
>that such an impact is *not* a sufficient cause for major extinctions.

Are you suggesting that such a cataclysmic event would leave NO evidence in
the fossil record? The energy released in such a collision are almost beyond
imagination (please see below). The impact would have a profound effect on
all life, and we are lucky that anything at all survived.
 
>At present there are effectivly *two* research issue of concern:
>       1. where was the K-T boundary impact.
>       2. was the impact *by* *itself* the primary cause
>          of the extinctions.

>What Dr. Holz was pointing out is that even #1 is not yet clearly
>answered - there are indications that Chixculub may *not* be the
>boundary impact.  Even the tsuname deposits are not, in themselves
>sufficient evidence of this.

Are you suggesting, then, that an object puncturing the crust of the earth
leaving a 120 mile wide gaping hole straight to the mantle turning the ocean
above into a boiling cauldren, raining glowing ash and molten rock on all
parts of the globe igniting fires everywhere would not leave prominent
residue in the geological record?  If you find iridium and ash deposits
widespread across the earth that hint of being contemporary to the Yucatan
crater it is highly likely that these deposits belong to the impact, since
iridium and ash had to have fallen all over the earth in copious amounts from
the impact. And this very layer coincides with the extinction of the
dinosaurs, adding further evidence that the impact occurred at this time.
 Yes, I know you are irritated that I keep referring to the extinction event
as a way to pin down the date of the strike since you believe that I am
trying to prove that the strike was cause of the extinction.  That is not
what I am trying to do.  You have mentioned that the strike may have occurred
8 million years before the KT boundary, and I am saying that it is absolutely
impossible for an event like the one that formed Chixculub crater to have
occurred without a severe effect to all life on earth.  Since there is no
sign of even unusual stress on the flora and fauna at this time, not to
mention no iridium or ash layer at this date, the strike could not have
happened at this date.  The only area in the geologic and fossil record that
hint of a strike is at this time is the KT event.  

>Also, to maintain #2 you must assert that the Deccan volcanism
>was a coincidence, while at the same time denying that the imapact
>could be a coincidence.

The Indian lava plains were not formed in a brief period of time, and would
not have left the sharp iridium spike that is seen in so many places.  Also,
their is little evidence supporting that this vulcanism had deleterious
effects on the fauna globally during the span of its activity.

 >Actually, T. rex had not yet evolved 8 million years prior to
>the K-T boundary.  That was the time of Albertosaurus and
>Daspletosaurus.

You misunderstood me.  I was saying that if the impact occurred 8 million
years before the KT boundary, that not only is there no evidence of it in the
fossil record (i.e. massive extinctions) at that time, but that life
continued to flourish and evolve during the time left into such creatures
such as T. rex indicating no measurable effect on life, which is not possible
with an impact of this size.

>Such a break up would only have occured if the object were a comet.
>Asteroids are much more solid, and would tend to remain intact.

>And if the impacter were a comet, it is not clear it would have
>produced a large crater. There is some reason to suspect that
>comets tend to break up high in the atmosphere.  First, there
>was the Tsunga explosion a few decades ago, and second there is
>the evidence that the Shoemaker-Levy fragments broke up quite
>high in Jupiter's atmosphere (though this is still not a settled
>issue - the data is still bein analyzed).
>[The Tsungas event produced no crater at all].

Again, sir, your argument is specious.  The Siberian explosion (that's
Tunguska explosion, by the way) was from an object that was at most 100 feet
in diameter, where the object responsible for the Mexican crater was probably
well over 10 miles across.  Giving you the most generous of measurements the
Mexican object had more than 150,000,000 times more mass.  It is highly
unlikely that a comet or anything else that large would have simply exploded
into nothing and leave no crater.  The object may well have been a comet, but
it need not be.  Any object of this size, sir, be it comet or asteroid could
easily be ripped apart by tidal forces.  Indeed our moon itself would be
ripped apart by Earth's gravity if it were close enough.

By the way, there is recent evidence of another, smaller impact crater in the
Pacific that is being claimed as a secondary impact.

Oh, and the Shoemaker-Levy comet demonstated exactly the opposite behavior
you suggest.  The impacts made with Jupiter were much more energetic than
almost anyone predicted, thus strongly suggesting that large cometary
fragments maintained their integrity.  Most of the break-up you mention
occurred due to tidal forces far, far outside of Jupiter's atmosphere and it
is similar to what probably happened 65 million years ago on earth.

V. S.