Tiers of Time and Trials of Extrapolationism 1311
unless, of course, you had a really good reason to believe that a diamond lay hidden
somewhere in that particular stratigraphic haystack.
This method of hyperintense sampling in optimal places has been applied, with
great success in validating substantial, even fully maintained, abundance right up to
the K-T boundary itself for two groups whose ostensible petering out had provided a
mainstay of empirically based opposition to catastrophic mass extinction—
ammonites as affirmed by Peter Ward's work in France and Spain (Ward, 1992), and
dinosaurs as indicated by collections of Sheehan et al. (1991) in Montana and North
Dakota. Seek and (perhaps) ye shall find, but in a real world of such limited time and
opportunity in scientific careers, one does need a theoretical license, as well as a
landowner's specific permission, to seek.
Despite my personal excitement at the theoretical and practical import of the
impact hypothesis, I must confess my initial surprise at a statement that historian of
science Bill Glen made to me in the early 1990's. For he asserted that the reforming
power of the impact theory would surpass even that of Plate Tectonics in the history
of geology. (And one cannot accuse Glen either of sour grapes or parochialism, for he
not only wrote the book on "living" history of science for the impact debate (Glen,
1994), but had previously written an even more highly acclaimed history in progress
for plate tectonics as well (Glen, 1982). Now I still don't fully agree with Glen, if
only for two primary reasons:
First, despite all its successes in 20 years, the Alvarez scenario still applies, with
proven power, only to the single event of the K-T mass extinction. None of the other
four great mass dyings show clear iridium spikes or other evidence for triggering by
impact (although some of the smaller extinction events have been more plausibly
linked to possible impact). Thus, the Alvarez scenario remains a historical
explanation, however elegantly affirmed, for a single event, and not a general theory
of mass extinction. (And, as I came to know and understand Luis Alvarez late in his
life, I rather suspect that this situation would have frustrated him intensely, for, as a
theoretical physicist by trade, he remained committed to the view that science can
only attain its true goal by establishing general explanations rooted in the spatio-
temporal in-variance of natural law. To learn that he had become godfather to the
contingent explanation of a great event, and not to the formulation of a general theory
of mass extinction, would have left him unamused.)
Second, even though we now have confidence in the factuality of impact as a
trigger for the K-T extinction, we still cannot specify a satisfactory "killing scenario"
to explain the timing and differential susceptibility to dying among life's various
taxa—a scarcely surprising circumstance, given the complexity of the event and the
potential number of dire consequences that impact might unleash, but still a damper
upon any feeling of full satisfaction. Indeed, I remain amused by how the competing
(and, to be sure, partly complementary) ideas follow the canonical scenarios for
disaster in Western culture—the ten plagues of Moses. And whenever our scientific
preferences so clearly match