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Note: Tunguska was not an impact.  The probable comet or ice body 
exploded at a considerable distance above the planet, probably 6 km
when internal heat buildup became so great that the forces holding it
together were overcome.  There are impact craters in Siberia from a
1947(?) event however.  

Another important aspect of the K-T event is the fact that the rocks at the
impact site were evaporites and limestones.  The evaporites contained
lots and lots of sulfur (or is it sulphur?) and the limestones, obviously,
carbon.  These constituents could have added a great deal of material
that would have been far more deadly than a hit on a granite mountan. 
Acid rains and vast CO and CO2 releases would have resulted. Yet
another important consideration is that there are three 65 MYO impact
sites. Possibly as a result of the object breaking up a la Shoemaker-Levy
9.  Manson impact and another Siberian impact crater >100 km diameter
are evidences thereof. Aside: Why do these bodies have such a
tendency to strike Russia? 

I think there's a lot more to the impact theory than just a BB hitting a big

>>> <Dinogeorge@aol.com> 08/11/98 09:23pm >>>
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,
 important, we have extremely good information on the timing of these
 events. As far as we can tell, within the bounds of error, they occur
 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
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
the same time that you take a shower, within known error bounds; you
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 simultaneous)
exactly the same time that something like half the species on earth
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
gunman's bullets entered their bodies.

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

Well, you should go back and read the papers, and without a jaundiced
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
of 1908 or the much bigger impact that gave us Meteor Crater in Arizona.
all know this, and we're not talking about such "puny" events.
<< Or, they propose scenarios that would have killed everything on the
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
that fed on them).  Point is: everything would have died.
 The ecosystem would not have been devistated, it would have been

 Nothing would survive.>>

This is indeed what would happen if an asteroid the size of Texas or
were to hit the earth at a cosmic velocity. Fortunately, these seem to
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
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 organisms
without killing everything.>>

Life is pretty tenacious, and asteroids big enough to kill off >everything<
are gone from the inner solar system. What are left among the truly
items are asteroids in the 5-10km size range, and comet nuclei from the
Cloud and the Kuiper Belt. (Comet Hale-Bopp was hefty enough to have
terrific damage had it hit the earth.) These have the potential to destroy a
good deal of life on earth, particularly us rather delicate multicellular
organisms, but I doubt whether they would have the energy to roast
<< Any in-between scenario would have to explain why the extinction
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
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
enantiornithines die?>>

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

I agree that these interesting facts require explanation. But as in my
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 killed
>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
that fell from the sky.  Get a globe, your standard American 12" diameter
globe will be fine for my example.  I have heard estimates of the size of
rock from between 6 and 10 miles across.  That means that with the 12"
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
relative velocity. An asteroid or comet colliding head on with the earth
be traveling at something like 50 km/sec--much faster than earth-escape
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
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
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
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<
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
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
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
pieces of the Yucatan peninsula were blown out to the other side of
because we've found them there. What else might such a blast have

We've observed the effects of a comet impact on Jupiter; the individual
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

Now, suppose the K-T asteroid had a companion, or was a "double" or
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
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
time) within a couple of days of one another. What then? (I'm not saying
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."