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Re: craters and the k/t (Norm King)
Sender: "King, Norm" <email@example.com>
Subject: Re: craters and the k/t
Bonnie Blackwell said (8/18/96; 1:07p):
>someone commented that the k/t event might not have been due to a
>meteorite but rather a comet, which left no crater. only problem is
>that you have to explain the approx 100 m wave that left tsunami
>deposits all over the gulf of mexico region (haiti, s. texas, alabama,
>jamaica ...). that presupposes some sort of large impact. as does
>the debris in chixiculub (sp?).
I think the presumed tsunami deposits are actually more in dispute than
the subsurface feature that is hypothesized to be the impact crater. The
tsunami deposit critics believe that the deposits in question were more
likely (or at least _as_ likely) formed during a lowstand of sea level
with its attendant erosional effects. They claim that similarly low
stands of sea level at other times and in other locations have produced
similar deposits. While this assertion merits attention, I think the the
K-T tsunami/lowstand deposits are _not typical_ of lowstand deposits
elsewhere. Of course, sea level lowstands must have been world-wide, and
deposits of this nature at the K-T boundary are known only from the Gulf
of Mexico region. Conversely, I believe deposits with these particular
characteristics in the Gulf region have been found _only_ at the K-T
boundary. Both observations are consistent with a K-T tsunami. However,
neither observation is excluded by the lowstand hypothesis.
Recently there was a discussion of people assuming that the Chicxulub
crater is indeed an impact crater before even going there to study it.
While the interpretation of the feature must always remain an
interpretation, and hence open to question, there it is certain that
_something_ is there in the subsurface. It just happens to be so close
to the K-T boundary that its position is indistinguishable from that
level. The data suggest a classic impact crater, with many (all?) of the
subtleties that should be observable for a buried impact crater. People
who know how to assess these things claim that the presumed crater is
large enough for the impact to have had an effect on the environment that
could have adversely affected life on a global scale.
Recently, a chunk of meteorite was brought up in a core from the eastern
Pacific from a location that would have been almost directly down range
from the impact, given the trajectory which had been calculated for the
impacting object based on independent data.
I don't know about the rest of you, but finally the number of
observations that fit together so nicely in the impact scenario become so
great that I find it impossible to believe that they are all
coincidences. The total becomes legitimately greater that the sum of the
parts. Science does work that way, to a certain extent. Theories become
organizing structures that allow us to make sense out of voluminous data
that are just random occurrences otherwise. Individually, any assertion
can be disputed. Just watch a courtroom trial to see if that isn't the
case. But when someone claims that each bit of evidence "superficially"
just "seems" to support a particular position, when actually the opposite
position is true, I find that unlikely. Scientific theories should be
regarded as conclusions in civil proceedings--the issue is decided on the
_preponderance_ of the evidence, rather than _beyond any doubt_. So,
while Chicxulub has not been unequivacally proved to be an impact crater
of a meteorite, that explanation is clearly supported at this time better
than any alternatives. But, hey, let's invite the critics to keep trying
to poke holes in the hypothesis.
Norman R. King tel: (812) 464-1794
Department of Geosciences fax: (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712 e-mail: firstname.lastname@example.org