Re: Religion (LONG)

[John Alroy <jack@homebrew.uchicago.edu>]

I'm sorry this is going to be a long one. I just got back from the  
evolution meetings, which explains why I didn't respond earlier to  
having my name taken in vain a few times. I will get to details  
later. First, I would like to make two general points that may  
explain why I seem to be so stubborn and close-minded about the K-T  
extinction event:

1) Empirical claim: the evidence really IS strong, at least with  
respect to the theory that a mass extinction did occur. The type of  
evidence I am used to looking at is statistical evidence for or  
against changes in extinction rates. The K-T extinction rates are  
far, far more dramatic than one would expect just because of normal  
background extinction rates going up a bit due to chance. I really  
feel that this is unambiguous and calls for some kind of a mechanism,  
and in this case the impact theory fits the geological data quite  
nicely. If it turns out to be wrong anyway, that says nothing about  
whether the extinction event itself occurred.

2) Sociological claim: the anti-impact school does seem to be losing  
out. Any new theory goes through phases of development, and here is  
one way to outline the process:

a) Everyone believes in theory X.
b) Somebody proposes competing theory Y. This is either ignored or  
recognized but dismissed with complete certainty by proponents of X.
c) More evidence for Y is gathered. Proponents of X attack this  
evidence AND try to show that X can account for the more reliable  
observations, and that Y fails to account for other positive  
evidence.
d) Proponents of X give up trying to explain anything in a positive  
way. Instead, they concentrate entirely on attacking the evidence for  
Y. Arguments focus on whether individual researchers are competent;  
whether individual analyses are reliable; whether ANY alternative  
theory (no matter how unrelated to theory X) could in principle  
account for the evidence; and on negative evidence ("where's the  
crater?").
e) Proponents of X either give up (flat-earthers) or refuse to give  
up but become completely marginalized in scientific circles  
(creationists).

This may be a flawed outline, but I think you see my point: I feel  
that if you just look at the KIND of arguments going back and forth  
about the K-T, they fall into phase d and not into phase c. Certainly  
we are not yet in phase e, and I am not trying to insult the  
gradualists/anti-impact people by equating them with creationists!!  
Also, you could make a case that the anti-impacters really are  
advocating a volcanic theory for the extinction, e.g., with regard to  
the shocked quartz, iridium (and other trace element) anomalies,  
tektikes, Chicxulub crater, "tsunami" deposits, and extinction  
itself. But then you have to recognize that there are TWO anti-impact  
theories at work here - volcanic extinction, and gradual extinction;  
that these theories are mutually incompatible; and that the SAME  
people are advocating both of these theories at the same time. The  
important point is that claims about this or that being "gradual" or  
"volcanic" seem to me like point-by-point attacks on the evidence  
that are not really intended to support an alternative theory.

A couple of specific points in response to earlier posts.

Stan Friesen: "the abundance
of dinosaur remains drops sharply a few meters below the siderophile
layer (aka boundary clay)."
        Again, please see Sheehan et al. (1991: Science 254,835) for  
the evidence against a gradual extinction pattern for dinosaurs. In  
situ dinosaurs are found "within 60 cm of the boundary" EVEN  
according to Williams (1994: J Paleont 68,183), who argues against  
the catastrophic model. This is less than an arm's length. I am  
getting a little frustrated that certain people (definitely not Ralph  
Chapman) don't seem to be aware of 1) the extreme rarity of in situ  
dinosaur remains, 2) the Signor-Lipps effect , 3) the fact that  
taphonomic regimes are wildly variable and not fully understood in  
terrestrial sediments, and 4) the fact that we are talking about 60  
cm, not 60 m or 600 m. Most "good" stratigraphic data for fossils are  
on the scale of meters, not centimeters.

Holtz: "Evidence of impact DOES NOT EQUAL evidence of extinction...  
The evidence for impact causing the extinction is, of course, the  
weakest,
and entirely circumstantial."
        Any argument "A caused B" has to show that A happened; that B  
happened; that A happened before B and in the same place; and that A  
and B are associated with each other beyond the expectations of  
chance alone (and maybe other things!). Therefore, by definition the  
evidence for an impact and for catastrophic extinctions must be much  
stronger than the "evidence" for a causal connection. However, I  
would like to point out that all of my A and B conditions seem to be  
met in this case (if we can agree on the argon dates and the  
Chicxulub crater being a crater and the extinction being real). If  
this is "weak" or "circumstantial," what causal theory isn't?

Stan Friesen (earlier post): "The pattern of disappearance of many  
groups, including that
of the dinosaurs... does not fit that model..."
        I'm always surprised that my paleontological colleagues put  
so much emphasis on "predictions" based on speculation about the  
physiology, ecology, and life history of extinct and ancient forms  
like multituberculates and dinosaurs, when 1) the extinction data  
themselves are heatedly debated (what "percent" of multis really went  
extinct? nobody seems to agree); 2) the "predictions" are extremely  
debatable; 3) the statistical analyses of these "predictions" are  
inadequate; 4) the record FOR TERRESTRIAL VERTEBRATES isn't that  
great to start with; 5) we have no first-hand idea what a really  
large impact like Chicxulub would do to the global atmosphere and  
climate, and certainly no idea how ecosystems would respond to those  
changes. We have enough trouble predicting ecosystem response for the  
(only relatively) modest two-fold increase of atmospheric CO2 that is  
happening right now. The important point is that a really unusual  
mass extinction DID happen.
Another important point is that the marine invertebrate workers have  
found an almost completely non-selective extinction pattern for  
molluscs. This analysis suffers from few or none of the above  
problems with the vertebrate analyses, and a climate-driven extincton  
model fails completely to account for these data.

"Coincidences *do* happen, and bolide impacts are actually fairly
common on a geological time scale."
        See above sociological argument. Note that in terms of size,  
the Chicxulub crater is at the far end of the spectrum for "normal"  
bolide impacts.

"Well, last I heard, the supposed tsunami beds were highly
questionable - they were apparently both earlier than the
K-T boundary, and probably not tsunami beds."
        One place to look is the recent account of the Snowbird  
conference in Science (I don't have the reference right here, it's a  
recent issue). Participants in the conference went together to  
examine a "tsunami" deposit and came away agreeing that a very  
high-energy mechanism was needed to create it. The minority of  
nay-sayers were previously committed to the anti-impact school and  
EVEN SO simply said they needed more evidence before they could make  
up their minds. There was no question about the dating of the  
deposit.

"New evidence has come to light of intact latest Cretaceous
sediments *inside* the supposed impact structure."
        I posted on this before. The single published paper on this  
supposed evidence (Meyerhoff, in Geology) provides no documentation  
for the age of the "fossils" mentioned and is based on a log kept  
during the drilling of the core more than 25 years ago. The authors  
seem unaware of the possibility of reworking or misidentifications. 


"the abundance of teeth drops drastically several meters
*below* the boundary clay - at about the same level as dinosaur
bones become seriously scarce, the so-called barren zone."
        This is based on material from WITHIN deep channel deposits  
in the Hell Creek. These channels appear to be earliest Paleocene  
(based on the mammal fauna; see D. Lofgren thesis), and the fall in  
abundance is perfectly in accord with the taphonomic "moving window"  
model of reworking. 


"Yep, so what?  All that shows is that the marine extinctions
were relatively abrupt...
I am *not* going to repost my summary of the evidence that
extinctions in general are *multicausal*, and usually associated
with flood basalt style volcanism."
        Multicausal models that casually dismiss evidence in this way  
are dangerously unparsimonious. Parsimonious theories try to account  
for ALL of the data in a SIMPLE way. Parsimony is the only reasonable  
criterion to apply in this debate.

I agree with Ralph Chapman's call for civility and open-mindedness  
and I hope the above doesn't come off as a flame - it's not intended  
that way. Cheers...