[meteorite-list] Re: Multiple Impact and 73P(was..More Evidence Chicxulub..)

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun Apr 2 00:15:05 2006
Message-ID: <012701c6552b$2e33f6f0$cce48c46_at_ATARIENGINE>

Hi, Doug and Interested Parties

    The reason that I put Smits' website URL
in my post:
<http://www.geo.vu.nl/~smit/csdp/debates.htm>
is that he very specifically and in great detail
"dissects" the quality of her work, which is a
polite way of saying that he rips it apart as
incompetent, a favor which Keller returns by
criticizing the abilities of Smits & co-workers
in turn.
    While there have been "disagreements" aired
over Keller's assertions, they are, well, polite (if
chilly), but the Smits-Keller exchanges are far
from "chilly." They're pretty much of a barroom
brawl and fairly entertaining.
    Smits' website links out to pages and pages
of photos of cores and thin sections, with Keller's
interpretation in one box and Smits' in another.
For example, he goes to the specific sites where
Keller & Co. took stratigraphic columns and
photographs the entire layer, and you can clearly
see (even me) that the entire strata is churned
and scrambled, making it a lousy place to sample
if you want demonstrate a undisturbed depositation
sequence.
    As for "her paleontological expertise," look at
his pages showing her own sections of the foram
fossils she says prove her case and read his analysis.
I posted the link hoping that someone (on the List)
with more expertise than I might have an opinion.
Keller & Co. don't seem to be arguing for MORE
impacts, but rather dismissing the role of impacts
altogether.

    Frankly, I found the chirpy sentence in the press
release --- "Even giant impacts aren't necessarily
global catastrophes..." --- really annoying. Giant
impacts aren't catastrophes? No kidding? I think
that's a colossally stupid thing to say... I'm going
to go out on a limb here and say that giant impacts
are a bad thing.

    There is considerable evidence for multiple
impacts, perhaps even aligned chains of impacts,
at the time of the Norian extinction, now dated to
214 million years ago. See:
http://www.sciencenews.org/pages/sn_arc98/5_16_98/bob1.htm
    The old and battered Rochechouart crater,
one of the chain of impacts, was recently discovered
to actually be only the inner ring of a multi-ring basin,
making it bigger than the Manicouagan and St. Martin
craters, a chain that stretches over 2700 miles, all on
paleolatitude 22.8N. Of course, there is a vigorous
chorus of geologists singing the coincidence song in
the traditional not-a-cause-of-extinction arrangement
about the Norian.

    Chicxulub is recent enough that the evidence
of any additional large impacts should be preserved.
What's not appreciated is that any (and all) large
impacts are fairly certain to be part of an episode
of many impacts. Early on, Chicxulub was characterized
as a "once in 100,000,000 year" event. It is more like
a "once in 1,000,000,000 year" event, based on its
estimated size.
    But expressing it as a statistical likelihood
conceals an important truth about the event.
This expression, in effect, implies that the
Chicxulub object occupied, for a long time, an
orbit with a very low probability of collision with
Earth until, finally, it's number came up. That is
an impossible scenario.
    Potentially Earth-impacting orbits have a
perturbation lifetime of less than 10,000,000 years.
Chicxi did not whizz around the inner solar system
for 4.4 billion years before hitting us. It couldn't have.
No, something put it here shortly before its terrible
accident. Given Chicxi's size and mass and the
difficulty of moving it around means that there
was a major shake-up somewhere else in
the solar system, likely to have influenced
far more than the one object.
    This contradicts our very human desire to
believe in an utterly stable solar system, even on
the longest time-scales. But the evidence is against
it. If planetary impacts were the result of the gradual
cleaning up of early solar system debris, we would
expect a monotonic decline in impacts, but the impact
record for the Moon shows a substantial upsurge in
impacts over the last 100,000,000 years. The
asteroidal collisional "families," long believed to be
ancient features turn out, on dynamic examination,
to be very, very recent. In the solar system, as on
bumper stickers, Stuff Happens.

    As for 73P, I wonder how many SMALL fragments
there are? Using Melosh's On-Line Impact Calculator
<http://www.lpl.arizona.edu/impacteffects/>
even a 100 meter chunk of ice version 1.0 would
produce a 10 megaton airblast 3 miles up. At 10 miles
from the epicenter, the winds would be 350 mph,
and (I quote) "Multistory wall-bearing buildings will
collapse. Wood frame buildings will almost completely
collapse. Glass windows will shatter. Up to 90 percent
of trees will be blown down; remainder will be stripped
of branches and leaves." A fractional Tunguska, in
other words. At 6 miles from the epicenter, the winds
would be 700 mph. The calculator seems to have a
"hole" in it; it won't calculate blast effects closer than
10 kilometers, but I'm guessing that the shock wave
there would kill you long before you started flying
at 700 mph...

    And this is a little, even trifling impact, unless of
course, you happen to be there at the time. If we knew
one was going to happen, maybe the author of the
press release that said impacts aren't catastrophes
should test that theory by standing there. Definitely
a life-changer, I would think.
    A chunk only 140 meters is still an airburst, but
the energy released is 270 megatons only 7000 feet
up. The devastation is much greater. A 150 meter
chunk reaches the ground in pieces traveling about
7000 mph. The impact energy is down to 1.6 megatons
but it leaves a strewn field with multiple craters, the
largest being about 1500 feet. A 200 meter ice chunk
impacts at 8 megatons and leaves a crater twice the
size of Arizona's Meteor Crater and 1500 feet deep.

    I'm really glad they've identified all the chunks
bigger than 500 meters (10,000 megatons and a
five-mile crater), but how many nasty little pieces
do you suppose there are?


Sterling K. Webb
------------------------------------------------

----- Original Message -----
From: <MexicoDoug_at_aol.com>
To: <sterling_k_webb_at_sbcglobal.net>; <meteorite-list@meteoritecentral.com>
Cc: <baalke_at_zagami.jpl.nasa.gov>
Sent: Thursday, March 30, 2006 2:58 PM
Subject: Multiple Impact and 73P(was..More Evidence Chicxulub..)


> Sterling W. writes:
>
> << Keller-Harting get lots of press, but nobody
> is convinced by them but them... >>
>
> Hola Sterling,
>
> That isn't entirely true. Gerta and her many European and Mexican
> collaborators have done much superb chonostratigraphic detective work and
> have been
> quite influential and have at least 15 years of solid science they've
> built. That
> the original theorists have every right to defend for their dramatic
> extinction scenario hypothesis is fine and healthy to a point, but the
> devil is hiding
> in the details, and Marcus Harding's work takes this to a new level by
> attempting a look further at morphology and chemistry like has not been
> done before.
> That is a good thing and these are exactly the type of folks needed since
> the geological record is so...errr...fragmented in the critical scheme of
> evaluating the hypothesis of the Nobel Prize winning Hollywood Impact
> Theory. This
> work is fresh research on a question that is so complicated that other
> researcher's won't touch since the possibility of successfully nailing it
> is slim
> after all of these 65.X million years. The fact the the press and more
> importantly the scientists themselves seem to be vocally passionate about
> their
> hypotheses does not excuse the true inconclusivity of the evidence for the
> accepted
> theory which merits keeping the issue on the table for the mainstream.
>
> Dr. Keller wisely sticks to her paleontological expertise, but if you have
> had an opportunity to discuss this with her you will know that her
> thinking
> regarding the killer asteroid scenario is quite refreshing and robust.
> The idea
> that multiple impacts ocurred doesn't seem to far fetched, and we can
> basically
> thank them for introducing it as potentially more viable and consistent
> based
> on top-notch fieldwork, not just astronomical mullings. If you want to
> dream
> up a nice scenario just look at the two dozen large pieces of Comet
> Shoemaker-Levy that pummelled Jupiter for over a week. Of course, Jupiter
> has pretty
> high-test fishing line compared to Earth and can land these beasts on the
> first
> try.
>
> So, let's have fun in about a month with some binoculars where you'll see
> two
> cometary fragments from Comet 73P Schwassmann-Wachmann 3 on May 12 and 14
> even from somewhat light polluted skies at nice, forgiving altitudes for
> backyard
> astronomers. Component C, apparently the main mass, passes 0.08 AU from
> earth first (on a sky trajectory before the 11th of May entering Vulpecula
> the Fox
> between the base of the cross of Cygnus the Swan and the second front leg
> of
> Pegasus the Flying Horse, and then less than two days later, at only 0.066
> AU
> just about leaving Vulpecula and entering Pegasus another huge mountain of
> component B will be whizzing by. Some of these chunks are in the 500
> meters to 1
> kilometer diameter range. There are over a dozen killer chunks detected
> so
> far. Some good food for thought while there's still food and thought
> available:) Too bad NASA lost the CONTOUR spacecraft a month after it was
> launched in
> July 2002. If the heliocentric booster maneuver hadn't been a failure, on
> June 18, Contour (That's COmet TOUR, not COmetS:)) would have made the
> most
> dramatic flyby of 73P than anything we have yet witnessed in our
> fortuitous
> livespans...
>
> There'll be a basically moon out for 73P as it passes Earth most closely
> so
> unfortunately the binocular view won't be very astounding and may only
> catch
> the largest C fragment. The best time to see the comet if you are serious
> is on
> May 7 or 8 at about 3:30 AM local time. During this time the main mass of
> the comet will be visiting the small, bright parallalelogram in Lyra the
> Lyre.
> Just find Vega in Lyra, then the second brightest star in the
> constellation
> and follow the side of the parallelogram where the Ring nebula is. The
> Comet
> will be brushing by it for some nice opportunities in moderate telescopes
> to bag
> the comet and nebula together...(and the nucleus will be visible in your
> binocular, though the Ring Nebula probably not unless you have some
> 30X100mm's)...
>
> Clear Moonless Skies,.
> Saludos, Doug
>
Received on Fri 31 Mar 2006 08:25:35 PM PST


Help support this free mailing list:



StumbleUpon
del.icio.us
reddit
Yahoo MyWeb