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There are several issues to consider in an impact, the first being
Newton's basic force equation: F = ma; or force = mass X acceleration.
As has been mentioned before, the material of the impacting object is
also a crucial element, as is the material & mass
Of the impacted object.  With both objects moving, the result is
additive.  We'd certainly have a more robust model if there had been a
recent collision.  One wonders, was the WHATEVER in Siberia a comet?
There's a good bit of information about the Krakatoa explosion, & the
effects were felt around the world.  BUT, it wasn't an impact; it was a
ballistic volcanic eruption, so the analogy with say - an asteroid
impact isn't a really great match.  :-)  Nevertheless, it is estimated
(HEAVY accent on ESTIMATED) that the Krakatoa explosion may have had the
force of 5 or 6 50 megaton hydrogen bombs.   
 Personally, I have wondered about the KT extinction theory a good bit.
When I was a young, "abused", underpaid, & overworked graduate student
in physics (LONG AGO!) I did some work for a Professor Wilson, who was
working on a longterm project with the 
American Geophysical Society, collecting & analyzing core samples from
the south pole.  I crunched gas phase numbers for months!
We also looked for organic material, minerals, etc.  Many of these
samples included Mesozoic material.  Some of these samples are STILL
being collected & analyzed.  We found what APPEARED to be evidence of an
alloy heavy impact from several of these samples.
I recall a high nickel, iron, & (not sure about this one), but I think
zinc content from a few samples.  The section of the samples that showed
this were Cretaceous.  The odd thing is, only a few of the Cretaceous
section samples showed these high metal contents.  From my gas phase
crunching, I also recall high oxygen content from Jurassic &
Cretaceous samples, higher than NOW, for instance.  I wasn't in on the
interpretation of these findings.  I was just a "grad grunt", but I
recall several theories being bandied about regarding the high
proportional O2 contents.  One was that the O2 level really WAS higher
then & another was that other gases tended to leach out or otherwise
escape from the sampled cores more easily.  But I recall some numbers.
I recall some Jurassic areas in samples yielding O2 contents that were ~
22% higher than our current level (at a comparable altitude).  There
were several theories about the metallic heavy sections too & one was
"an asteroid".  Whether or not this was
THE supposed KT asteroid, I don't know.
 However, I still find myself troubled by the selectivity of the KT
extinction theory.  IF most dinosaurs were endothermic or "metathermic",
were large endotherms more vulnerable? And, if so, why did the sub 50 kg
dinosaurs also die out?  Had most of them already evolved into birds?
Were there small nonavian species alive towards the end of the
Cretaceous?  I thought there were examples?


        -----Original Message-----
        From:   Dinogeorge@aol.com [SMTP:Dinogeorge@aol.com]
        Sent:   Tuesday, August 11, 1998 8:23 PM
        To:     Tetanurae@aol.com; dinosaur@usc.edu

        In a message dated 98-08-11 17:49:27 EDT, Tetanurae writes:

        << George Olshevsky wrote:
         <<We have a hole in the ground, we have lots of missing
animals, and, most
         important, we have extremely good information on the timing of
these two
         events. As far as we can tell, within the bounds of error, they
         Yes, yes, blah.  They happened at roughly the same time: so
what?  I brush my
        teeth at roughly thr same time I take a shower.  That doesn't
mean I brush my
        teeth while I'm in the shower.  You have a correlation, and
that's just it.>>

        As a matter of fact, unless you're peculiar, you do >not< brush
your teeth at
        the same time that you take a shower, within known error bounds;
you generally
        brush your teeth slightly before or slightly after you take a
shower. Your
        analogy breaks down.

        As I noted before, if the K-T asteroid impact occurred at almost
(I'll give
        you an "almost" here, although geologically speaking it is
        exactly the same time that something like half the species on
earth became
        extinct for some other, totally unrelated reason or reasons,
it's easily the
        most cosmic coincidence in the history of the universe. Like the
bystanders in
        my gunman analogy, who suddenly died of heart failure instants
before the
        gunman's bullets entered their bodies.

        << What you need is a positive cause of the extinctions that
would have come
        from rocks falling from the sky.  So far all I have seen are
        rediculous, ludicrus, or ignorant explanations.>>

        Well, you should go back and read the papers, and without a
jaundiced eye,
        either. The cause is >quite< positive.
        << They either pose a scenario which wouldn't have killed
ANYTHING because the
        nuclear winter or whatever would have lasted about a week and
would have just
        yellowed the figurative grass.>>

        This is probably what happens after >most< asteroid/meteor/comet
        They're not big enough to do more than local damage, like the
Tunguska impact
        of 1908 or the much bigger impact that gave us Meteor Crater in
Arizona. We
        all know this, and we're not talking about such "puny" events.
        << Or, they propose scenarios that would have killed everything
on the planet.
        Decades of freezing or baking temperatures that would have
either burnt,
        killed or froze every single plant, seed or spore on the planet,
not to
        mention phytoplankton, and the starving animals that fed on them
(and those
        that fed on them).  Point is: everything would have died.
         The ecosystem would not have been devistated, it would have
been destroyed.

         Nothing would survive.>>

        This is indeed what would happen if an asteroid the size of
Texas or bigger
        were to hit the earth at a cosmic velocity. Fortunately, these
seem to have
        been all used up 4 billion years ago, before life got a foothold
on earth.
        Something the size of Rhode Island once hit the moon and created
Mare Imbium.
        Doubtless the earth had its share of similar impacts after it
was formed.
        << There is no way that you could have killed off one group of
        without killing everything.>>

        Life is pretty tenacious, and asteroids big enough to kill off
        are gone from the inner solar system. What are left among the
truly dangerous
        items are asteroids in the 5-10km size range, and comet nuclei
from the Oort
        Cloud and the Kuiper Belt. (Comet Hale-Bopp was hefty enough to
have done
        terrific damage had it hit the earth.) These have the potential
to destroy a
        good deal of life on earth, particularly us rather delicate
        organisms, but I doubt whether they would have the energy to
        << Any in-between scenario would have to explain why the
extinction was SOOOO
        selective when the agent of destruction was so all encompassing.
Counter to
        George's claim to the contrary the rock from the sky supporters
DO have to
        explain why some things survived with no problems.  Why did
nautiloids go on
        with no problems, while ammonites didn't.  Why did neornithine
birds live and
        enantiornithines die?>>

        Who knows what problems the asteroid impact may have caused for
        They were probably decimated--they just weren't decimated
enough, like the

        I agree that these interesting facts require explanation. But as
in my earlier
        gunman analogy, you are arguing that, since asteroids obviously
didn't kill
        >everything<, the one that hit at the K-T boundary couldn't have
        >anything<. This, of course, is quite wrong, as I think I've
demonstrated. It
        certainly could, and it did.
        << Another thing I would like to point out to everyone is the
size of the rock
        that fell from the sky.  Get a globe, your standard American 12"
        globe will be fine for my example.  I have heard estimates of
the size of this
        rock from between 6 and 10 miles across.  That means that with
the 12" globe
        the rock that killed the dinosaurs would be between 1/110 and
1/66 of an
        inch!!!  This is bordering on microscopic.>>

        It is not the size of the object that matters, it's the kinetic
energy that
        determines how powerful the impact will be. You remember, KE =
        [without relativistic correction]? The energy increases with the
square of the
        relative velocity. An asteroid or comet colliding head on with
the earth might
        be traveling at something like 50 km/sec--much faster than
        velocity. And even if the asteroid were ten miles across, it
would still be
        the size of, say, San Diego. Hardly a grain of dust. All this
kinetic energy
        would be released within a few seconds at the impact point as
the asteroid
        came to rest: something like a few million to a billion or more
times the
        energy released in the Hiroshima atomic explosion. The asteroid
would be
        vaporized, along with a good chunk of terrestrial real estate,
pieces of which
        would be blown completely around the world.

        The highest-energy cosmic rays known to strike the earth pack
the wallop of a
        thrown baseball into a single proton. If you were hit by one of
these protons,
        it could knock you down (assuming it didn't just tear through
you but got
        stuck somehow). And how big is a proton relative to yourself?
>Far< smaller
        than the asteroid relative to the earth. Energy is the key
factor here, not
        just size.
        << And this tiny partical of dust is supposed to kick up enough
dust and rock
        to cloud up the atmosphere, block out the sun, then bake the
earth enough to
        cause massive firestorms!?  Give me a break!  Am the only one
that thinks that
        this is just slightly absurd? >>

        Probably. We know that pulverized asteroid landed everywhere
around the world,
        because that's largely what makes up the K-T boundary clay. We
know that
        pieces of the Yucatan peninsula were blown out to the other side
of Florida,
        because we've found them there. What else might such a blast
have done?

        We've observed the effects of a comet impact on Jupiter; the
individual pieces
        of the comet left earth-size holes in its atmosphere that may
still be
        visible, and the impact flashes were easily seen through
telescopes here on

        Now, suppose the K-T asteroid had a companion, or was a "double"
or "multiple"
        asteroid--two or more bodies loosely joined together, as was
Shoemaker-Levy 9
        before Jupiter's gravitational field tore it apart. Suppose
three or four such
        objects hit the earth in different places (one leaving the
so-called "Shiva"
        crater in the Indian Ocean, for example--also roughly dated at
K-T boundary
        time) within a couple of days of one another. What then? (I'm
not saying this
        happened, since I think one good-sized impact would have done
the job, but the
        possibility exists, and there's even some evidence for it.) "If
the right one
        don't get ya, the left one will."