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Re: Extinction (was:Religion)
Whoa! I thought things had calmed down a bit, but Dr. Schwimmer seems
to have taken offense. Before I start I should note that I have
passed my Ph.D. defense and finished my thesis but the paperwork
hasn't gone through yet, so I suppose you can still call me "Mr."
Alroy.
My comment about "well-articulated arguments" was directed towards
the VOLCANISM model for a mass extinction, not anti-impact models in
general. I wasn't aware of the Rampino papers, although it had
percolated into my consciousness that there really was such
literature out there to be found. As I had hoped, Stan Friesen had
the references on hand, and I thank Dr. Schwimmer for the added refs.
When I said "I'm not aware," I literally meant "I'm spacing on this,
somebody help me out."
I was jumping the gun when I said that Keller et al. "are trying to
show that there was no mass extinction"; what I meant was that they
are trying to show there was no sudden, catastrophic mass extinction.
Their arguments frequently revolve around whether, say, a 60-70%
species-level extinction in less than a meter of section is
"biologically important," which is what prompted me to say this. The
tone of Keller and Officer's articles is consistently negative and
that really was the point I was trying to get at.
My quote of the Kerr article was just that, a direct quote. Why slam
me over it? The occurrence of a seismically-produced tsunami on an
enormous scale exactly at the K-T boundary seems like an improbable
coincidence to me, but, of course, this sort of ad hoc, case by case
assault on the data is exactly what you should expect in phase d of a
debate like this.
Thanks for the references. I have checked the McLean letter, which
you said was "a good starting place," and found it to be very
telling. His main point is that Science published 61 pro-impact
papers from 1980 to 1993 and four "stricly nonimpact items" in that
interval, all before November 1989; plus one article that "hinted at
the possibility of volcanic influence in the K-T extinctions." He
then goes on to slam Science for violating the First Amendment (I'm
not kidding), and is rebutted by Daniel Koshland, the editor of the
journal, who points out that the content of Science largely reflects
what is submitted to it and what is going on in the field. I can
think of no better evidence for my original claim that the impact
issue had long been settled in favor of the idea that an impact
occurred at the time of a major mass extinction (debate continues
about cause-and-effect): 90% of the post-Alvarez literature has been
pro-impact. The fact that old arguments like the "Three Meter Gap"
(now called a 2 m gap, and actually a 60 cm gap, and I expect it will
eventually be a 1 cm gap and the anti-catastrophists will still be
arguing about it) continue to be recycled by people like Williams ten
or more years after the original debates is additional evidence for
this claim.
I am unaware of mammal faunas in the Lance straddling the K-T. I
would be very surprised if there were microvertebrate faunas without
mammals in this section, so I assume you are talking about dinosaurs
exclusively. Just for my information, what study has been published
showing a "gap" at the top of a continuous section through Lance-Fort
Union (or Polecat Bench, or whatever) contact? My records show
earliest Paleocene (i.e., Puercan) mammals in Wyoming only in the
Bighorn Basin, where the terrestrial vertebrate record is minimal (I
have exactly one, minor mammal locality in the local "Lance
equivalent"). I do have a recent reference on the Tornillo Formation
(Schiebout et al. 1987: J Geol 95,359), which specifically notes that
there is a 35 m barren zone devoid of known terrestrial vertebrates
that spans the boundary. Therefore, the Tornillo Formation has
nothing to do with this discussion.
It seems to me that Stan Friesen was correct in the first place in
noting that the only field area in which anything resembling a true
"gap" has been found is the Hell Creek area.
It's hard to believe that after all this discussion I still have to
field casual ad hominem attacks like "I believe Mike Williams has
spent a lot of time in the Hell Creek outcrop and has seen the
evidence first hand. Have you?" This has nothing to do with the
issue at hand, which was that Williams' article contained no new data
or analyses, just qualitative arguments. Your comment about my
"childlike faith" is similarly insulting and out of place. I have
previously had to put up with insults directed at my university and
my major advisor, which is completely inappropriate in a public
discussion. Have any of my own comments been similarly ad hominem?
Can we please agree to keep this debate from degenerating into pure
mud-slinging?
My point about sedimentation rates was that the MAXIMAL duration of
the 2 meter "gap" was on the scale of 40,000 years, UNLESS there is a
major hiatus in that interval. I have seen no indication that anyone
believes there is such a hiatus, in which case my calculations are
completely reasonable (they also agree with a separate but similar
calculation made by Friesen). General words of caution about
interpolating sedimentation rates don't address the fact that this is
a valid UPPER estimate given the absence of a hiatus. My original
purpose was to note that a 100,000 - 250,000 year figure for the 2 m
"gap" was too high.
My five-phase model for the acceptance of new theories pertained to
the ACCEPTANCE of new theories, not the rejection of new theories. I
thought this was clear from what I wrote but now I think I should
have made this more explicit, because Stan Friesen made a similar
comment. In my opinion a rejected theory never moves beyond my phase
c, and the impact-based catastrophic mass extinction model has now
moved to phase d (Friesen doesn't agree and since my argument was
merely impressionistic I have nothing to say about that). I just came
across an interesting quote in Raup's Nemesis book to the effect that
61% of 500 professional geologists and paleontologists in a 1984 poll
accepted the evidence for an impact at the K-T. This figure would
surely be much higher in 1994, because there wasn't even a decent
candidate crater 10 years ago. I also just found a chapter in his
book entitled "The Three Meter Gap and Other Evidence," which was
written in 1985! We are not exactly going over new ground here.
Raup didn't come up with the Nemesis model for periodic mass
extinctions; that's an astrophysicist's responsibility. He came up
with the statistical data for the extinction pattern and wrote a
popular book describing the course of the debate. The Nemesis model
relied on 1) statistical analyses of extinction data, and 2) showing
that many or most of the "right" extinction events were related to
asteroid impacts. Because the data are hard to get, the latter is
still an open question. The statistical analyses were equivocal and
I'm actually a little surprised there hasn't been more on this now
that the genus-level data are available (the original analyses were
based on family-level data).
I think the Kerr quote on the tsunami deposit in Mexico speaks for
itself. The point is that a VERY HIGH-ENERGY mechanism would be
needed to explain the deposit, and such a mechanism isn't provided by
marine regression or Deccan Traps volcanism models.
The comment on Meyerhoff is hardly worth replying to. At this point I
am starting to get the impression that Dr. Schwimmer believes that
"expert opinions" are not to be questioned by anyone, regardless of
how old the data are or whether they are even published! I am not
comfortable with a vision of science that views decision-making as an
exclusive right of empiricists with so-and-so many years of field
experience, and theorists as beneath contempt. This is made clear in
Schwimmer's insulting comment that I should "try doing some alpha
field work" myself, as if this would prove to me that simply SAYING
that a pattern exists is plenty of scientific evidence for it, as
long as the scientist speaking is a field worker. Personally, I am
very skeptical of any faunal data that 1) are unpublished, and 2) are
nearly 30 years out of date, and I say this because I have personally
compiled 3000 faunal lists and attempted to bring them up to the most
current taxonomy. What I find over and over again is that faunal
lists from the 1960's and earlier are almost completely unreliable at
the species level prior to being corrected.
I agree that the K-T marine regression may have been an important
contributing factor in the extinction event. However, it fails to
explain the extremely rapid and severe extinction of terrestrial
mammals and plants at that time. Regressions of similar magnitude
occurred several times during the Cenozoic, and there is no evidence
for a mass extinction of mammals ANYWHERE in the Tertiary record of
North America! Why would marine regression cause such serious trouble
for terrestrial communities at the K-T boundary but never again for
nearly 65 million years? I genuinely find this intriguing.