Catastrophic Extinction?

[Jon Stanley <jstanley@fred.fhcrc.org>]

        Please forgive me if this subject has already been beaten to 
death, but I am relatively new to this mailing list.

        I have been involved of late in a discussion on America On-Line 
with Leon Jaroff, a senior editor at TIME magazine, concerning the 
extinction of the dinosaurs.  My position (as merely an interested 
layman) has been that a meteor impact at the end of the Cretaceous may 
have contributed to the extinctions, but that the evidence for a sudden, 
catastrophic end (i.e., that the meteor was the predominant cause of the 
extinctions) is lacking.  I have cited the low diversity of fossils seen 
in some of the major beds near the end of the Cretaceous (which indicates 
that dinosaur ecosystems were not in good health prior to the impact), 
the evidence that other well-documented meteor impacts (such as that in 
the late Triassic) had no such effect on the dinosaurs, and the fact that 
there are no fossils within about 100,000 years of the iridium layer 
(which may simply be circumstantial evidence).  Furthermore, there is the 
fact that certain whole groups, such as fragile fresh-water inhabitants 
(frogs, etc.), were virtually unaffected by the impact.  This all seems 
to me to point toward a gradual, drawn-out process of extinction rather 
than a catastrophic end.  (My sources for information have included 
writings by Robert Bakker, Greg Paul and Jack Horner.)

        Mr. Jaroff, however, has stated that "the catastrophe is pretty 
well established," and that "opposition to the asteroid (or, more likely 
the comet) theory is now largely confined to a dwindling number of 
paleontologists."  He has cited support for the catastrophic theory from 
geologist Eugene Shoemaker, of the U.S. Geological Survey, and has used 
the examples of paleontologists Steven Stanley and Clemens to show that 
paleontologists are gradually (and somewhat grudgingly) coming to favor 
the theory.

        Is Mr. Jaroff's position accurate?  If so, it seems to run 
counter to the writings of almost every paleontologist I have read, and 
the evidence discussed in those writings.  I was hoping that, if it 
wasn't too much trouble, someone out there more knowledgeable than I 
could briefly summarize the current state of meteor impact theory.  If I 
am mistaken, or if I have been left behind by new revelations on the 
extinctions, I'd like to know, as I think would Mr. Jaroff.

Thank you,

Jon Stanley

P.S.  Another individual involved in the discussion who shares my 
position has stated that dinosaur fossils have been found at least 
500,000 years above the K-T boundary that cannot be attributed to 
redepostion.  His source is an article by J. Keith Rigby, Jr., in 
_Dinosaurs Past and Present Volume II_.  I have never heard this, and am 
skeptical of the claim.  Can anyone confirm or deny it?

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   _______  Jon F. Stanley                       | "...bred amongst the   
^--\     |  jstanley@fred.fhcrc.org              | weeds and tares of mine
 \ W     |  Fred Hutchinson Cancer Research Ctr. | own brain"             
  |__-----  Seattle, Washington                  |         - Thomas Browne
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