[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]


>I think you're assuming some of what you hope to prove. Is there
>any evidence that the Chicxulub impact reached all the way to the
>mantle, as you describe? (I raise this because some of the most
>dramatic effects you're invoking here seem to require mantle
>material as distinct from dust and ash.)

>Also, you can't simply say that it's impossible that such an impact
>wouldn't lead to massive extinctions until/unless we've established
>the connection between a cometary or asteroid impact (at _some_ point
>in Earth's history) and extinctions. (I'm inclined to think that there
>would be some damage, but how widespread it would be is still in =


and Thomas R. Holtz, Jr. writes:

>Check out the appropriate stratigraphic data.  The Chixculub impact only=

>goes down into mid-Cretaceous anhydrite deposits, not "straight to the
>mantle" at all.  The bottom of the crater was found long before they
>recognized it as a crater.

Whether or not the body penetrated to the mantle is not at all important
as others have written, it very well could have, depending on the thickne=
of =

the crust at the impact site and the material the body was composed of.)

What is important is the amount of energy the impacting body was carrying=
, so
I=92ll try to illustrate this enormous quantity as clearly as possible.

For the sake of simplicity, let=92s assume that the body is spherical in =
with a
diameter of 10 miles.  This gives it a total volume of 523.6 cubic miles =
or =

2.1825e12 cubic meters.  A comet would probably have a density at or some=
less than the density of water, while an asteroid would have a much highe=
but, for the sake of simplicity, let=92s assume that the body=92s density=
 is that
of room
temperature water.  This would give the body a mass of 2.18e15 kg.

To make a crude estimate of the body=92s impact velocity, let=92s assume =
that the
is on a highly eccentric ordit -- as comets and dinosaur-vaporizing-aster=
are want
to do  In such an instance, the body is likely to smack into the earth at=

near earth=92s orbital velocity of about 67,000 mph (29,800 m/s or 97,800=

ft/s).  To =

put this enormous velocity into perspective, the fastest muzzle velocitie=
claimed for legal high powered rifles are around 4,000 ft/s -- handguns
are often below 1000 ft/s -- so our 10 mile body is moving towards the ea=
at over 24 times faster than the fastest bullets.

This yields a kinetic energy for the body of about 10^24 J.  If you=92re
with this notation that=92s 1,000,000,000,000,000,000,000,000 Joules whic=
probably still doesn=92t mean much to you, but it=92s close to the energy=

by 12 billion Hiroshima type atomic bombs.  So you could take every man,
woman, child, baby, dog, cat, cow, horse, pig, goat, spotted owl (and eve=
endangered species) and strap each individual to their own personal A-bom=
b, =

and, upon detonation, be fairly certain that you at least caused the
of those species.  In fact, I think it wouldn=92t be going too far to say=
the cities
would be completely sterilized of all life -- even the lowest forms of li=
like =

politicians and lawyers.

If 12 billion A-bombs means nothing to you, take this final comparison.  =
The =

impacting body has the same amount energy as if you would coat all of the=

land areas on earth (including Antarctica -- we wouldn=92t want any nasty=

penguins overlooked) with TNT so that each and every single square meter
of land, hill, valley, mountain, whatever, is covered with 1.4 tons of
Just in case you don=92t have a good feeling for what 1.4 tons of TNT can=
the Oklahoma City bombing used no more than the equivalent to 1 ton of

That=92s a lot of energy!

But, I don=92t want to seem to infer that the detonation of a global coat=
would be exactly like the impacting of our 10-mile-wide-body.  In the cas=
e of

our colliding bollide, all that tremendous amount of energy would be
initially =

concentrated in a relatively tiny area -- in your mind try to imagine
all of those A-bombs (or all of that TNT) and piling them on an area with=
in a
5-mile radius of the studio that makes that Barney show and in blissful g=
detonate them and you will have a little better idea of the impact event.=

There is little question that more than a few species would still be
especially when you consider how many species are parts of very delicate,=

easily upset ecosystems.  The extent of that damage can be seen at the KT=


It is important to realize, that it doesn=92t matter what the bollide is
composed of
to carry this much energy.  The only thing that matters is the mass of th=
object and its velocity (KE =3D 0.5*m*v^2).  It could be a solid block of=
or =

a flying marshmallow, as long as it has the mass and velocity we describe=
above, it is going to have the energy we arrived at.  A different consist=
will only mean a difference in how that energy is transferred to earth.  =
object like an iron meteorite will expend more energy penetrating the ear=
crust than a softer, more volatile, object like a comet.  A comet is more=

to expend more energy as heat, shock waves, etc. and make a shallower
crater.  This can actually be even more destructive than the damage
caused by deeply penetrating iron or stony body because more of the
comet=92s energy is dumped into the zone we live in.

So, it really doesn=92t matter if the object penetrated to the mantle or =
the object were to penetrate to the mantle it would expend more energy
in penetrating the crust, but would also allow some of the mantle=92s
energy to escape.  If the object didn=92t penetrate to the mantle it woul=
dump more of its energy as explosions and heat.  And since the energy
of the impacting object alone is way more than necessary to obliterate =

ecosystems, it is really not necessary for the mantle to be exposed to
sustain my original point:  That one of the signatures of the impact will=

be catastrophic extinctions in at least the same hemisphere as
the impact, and since this happens only at the KT boundary (which
corresponds with the other signature: the iridium-ash layer) then the
impact must date from the KT boundary, and the iridium layer must
belong to it.

Vicki Rosenzweig adds:

>Third, nobody (as far as I know in this discussion) is denying the
>connection between the impact and the iridium layer--the question is
>how we can be sure that the impact, rather than the Deccan basalt flow
>or some other cause, led to the K-T extinctions.

You must not have read your e-mail very closely, or perhaps these
messages were sent only to me, I didn=92t check, but of the arguments
I have received has centered around whether or not the Yucatan
crater was even near the KT boundary:

as Thomas R. Holtz, Jr. demonstrates:

>... Actually, T. rex evolved several million years after the impact, =

>if the Meyerhoff dates are correct (which is still a possibility).
>If the dating is correct, than it would show that an impact which =

>generates a 120 mi crate would [not?] be sufficient to
>kill off large groups of animals, "back-of-the-envelope" equations

>The Manson crater is dated very securly at the early part of the late
>Campanian, the same age Meyerhoff et al. claim the Chixculub is dated at=
>If so, than multiple large impacts would immediately precede the epoch w=
>the highest known dinosaurian diversity in the Mesozoic.

John W. Atwood writes:

>"all over the earth in copious amounts" is not really demonstrated by
>the stratigraphic record.  The iridium layer is not always easy to
>find, even in areas of continual sedimentation.  Often it is determined
>only by using a microscope, and/or chemical analysis.  Yes, the TRACE
>has been found in many areas around the earth, but real evidence of a
>major or complete global involvement is lacking, leaving plenty of room
>for questions on both sides.

Frankly, I=92m surprised that you would try to make this point.  The prop=
conditions for fossilization are pretty hard to come by, as I=92m sure yo=
know.  So a copious amount of iridium and ash falling all over the earth
does not mean a big, thick layer of iridium and ash in the strata.  And, =
in no way meant to imply that the layer was uniform everywhere.  In some
places I=92m sure it was tens, or even hundreds of feet deep, while at ot=
it may have been only inches or less.

Finally, Mickey Rowe, who seems to have taken all that I=92ve said a litt=
le too
personally, has referred several sources to me on different occasions in
what are apparently attempts to both enlighten and insult me.  Fortunatel=
on Friday, Peter Sheehan, Paul Sparks, and Larry Bowlds addressed all
of Mr. Rowe=92s concerns with far more eloquence and authority than I =

could hope to do myself.

Van Smith