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Re: craters and the k/t (Norm King)

Sender: "King, Norm" <nking.ucs@smtp.usi.edu>
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:  nking.ucs@smtp.usi.edu