[meteorite-list] New KT asteroid injection theory PART TWO

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 6 Sep 2007 20:09:31 -0500
Message-ID: <021e01c7f0eb$bf773570$2850e146_at_ATARIENGINE>

Hi, Paul, EP, List,

    The San Francisco Chronicle article Paul cited
includes reaction and perspective from Richard Muller.
Yes, Muller's 2002 study does shows a big increase
in cratering 600 million to 400 million years ago, and a sharp
risxe in the last 100 million years, and that result has been
confirmed by many other studies, but the increase does
NOT seem to be from comets, but from asteroids instead!

    There was another and bigger asteroid breakup at that
time, much bigger than the one 160 million years ago, that
could well be responsible for the large increase in impacts
(3.7+/- 1.2 TIMES as many as previously, in the "quiet"
times a billion years ago).
http://muller.lbl.gov/papers/Lunar_impacts_Nemesis.pdf
The meteorites from this big breakup have been found
as Ordovician fossil meteorites!
http://www.psrd.hawaii.edu/Mar04/fossilMeteorites.html

    The fall frequency implied by the fossil meteorites
is at least seventy times today's rate of fall, and possibly 170
times greater! The peak of the activity was during the
Ordovician period, about 480 million years ago. The most
likely breakup event is the fragmentation of L chondrite
parent body (still the most common type to fall on the
Earth) which we know must have happened within the last
billion years, with about 570-600 million years ago as the
most likely time.

    The peak of falls at 480 million years ago was very
"peaky." CRE ages of the "fossil" meteorites show very
short space exposures. I suspect the meteoroidal equivalent
of the "Kessler Syndrome" in the wake of the breakup.
http://en.wikipedia.org/wiki/Kessler_Syndrome
If an collision products collide faster than their orbits
diverge, you get a "flurry" of fragmentation. An object
as big as L-chondrite parent body, 200 to 300 km in
diameter, does not break into millions of little pieces
in one jump. It takes lots of subsequent collisions.

    A 200 kilometer body contains enough material to make
thirty 64-kilometer bodies, each in themselves carrying
enough energy at average "meteoroidal" velocity to release
the equivalent of 10^27 joules in the (now molten) crust
of an impacted planet.

    The L chondrite parent body would have to have been
that much larger than the Baptistina family parent body. About
half the meteorites that fall today are L chondrites and many
of them were shocked 465?15 million years ago. That there
should still be so many falling after half a billion years implies
a very large supply to begin with!

    That vaguely Cambrian time period just before the
Ordovician saw a lot of major nasty events on this planet:
the Earth had three long and massive ice ages (including
the coldest ever one) in about 150 million years; the planet's
obliquity changed by 90 degrees in a few dozen million
years; all sorts of "never-happen" events happened! It's hard
to avoid the thought that something fairly violent was going
on in that short period of time.

    480 million years ago was a rough time for other bodies
than the Earth. When Magellan finished the fine-scale radar
map of Venus, "crater counters" were called in. Dating a
surface by its crater count and distribution of sizes is a
highly refined specialty; you don't "do it yourself." They
all agreed: the surface of Venus was 480 +/- 60 million
years old.

    No Venus expert liked that answer. No Venus expert
accepted that answer... at that time. Now, after a decade or
so of denial, you'll find that apparent fact creeping back
into the literature. There is no particular reason to doubt
the validity of the crater count method that we trust for
EVERY other solar system body, a method we continue
to use and refine with NO problems.

    It seems a remarkable coincidence that the surface of
Venus should date to a period of very intense bombardment
if that bombardment was not, in fact, the cause of a complete
re-surfacing of the planet. (One of those harmless looking
L chondrites in your collection could be a cousin to a
Planet Killer.)

    Back to the Chicxulub Rock. One of Bottke's own papers:
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1634.pdf
suggests the average life time for a big NEA is about 10,000,000
years, so its orbit must have evolved in stages brought on by
a number of orbit-altering encounters over roughly 90,000,000
years before Chicxulub Rock got into position to whack us.
(And obviously it must have been, prior to impact, an NEA
-- you gotta get NEAR the Earth in order to hit the Earth!)

    There were a lot of such objects. Bottke estimates that there
were 300 chunks BIGGER than the six-mile Chixulub'er (1000
1-milers or better). What's surprising is not that we got
whacked by one but that we got whacked by ONLY one!
There has been an increase in impacts over the last 100
million years, and possibly over the last 200 million. Whether
that is entirely due to the Baptistina breakup is completely
unclear. (No offense, but Bottke may be a little biased
about his discovery; it happens.)

    The question remains: where did the impactor that
broke up the proto Baptistina Come From? Baptistina
is fat and happy for 4400 million years and then --- Smack!
Maybe the 35-km Baptistina impactor was a chunk of the
L-chondrite parent body?

    Can a collection like the entire Asteroid Zone remain
relatively stable and then begin an era of increasingly rapid
collisional generation of new objects in erratic orbits, like
a long-term Kessler Syndrome? The impact frequencies
for the entire history of the solar system in Muller's paper
(URL above) show lower rates between 3.2 billion years
ago and 600 million years ago. In fact, in a "static" solar
system (one which produces no "new" big impactors),
the impact rate curve should just tail away to the right
exponentially and disappear. I see no "spike-like" traces
of previous big asteroidal breakups. Maybe it just takes
four billion years for them to get going?

    See, there's no end to where these things lead...


Sterling K. Webb
-----------------------------------------------------------------------
----- Original Message -----
From: "E.P. Grondine" <epgrondine at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Thursday, September 06, 2007 10:56 AM
Subject: [meteorite-list] New KT asteroid injection theory


Hi Paul, list,

The problem with this new theory is that what hit
appears to have been a comet:

http://www.scn.org/~bh162/meteorite.html

Furthermore, the injection mechanism has been
identified as gravity perturbations due to our solar
system passing through the plane of our galaxy, which
theory agrees with 26 million year chaotically
cyclical pattern in mass extinctions:

http://www.csmate.colostate.edu/cltw/cohortpages/viney_old1/massextinctionchart.html

http://users.tpg.com.au/users/tps-seti/crater.html

The physical evidence would seem to validate Clube and
Napier's and the Italian dynamicists' work.

Morrison's "Nemisis" hypothesis and Firstone's new
hypothesis both appear to be mistaken, and it is most
likely that these gentlemen's are as well.

E.P. Grondine
Man and Impact in the Americas






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Received on Thu 06 Sep 2007 09:09:31 PM PDT