In this case, the Alvarez theory suggested little more than
hard work.
So why wasn't the effort expended before? Paleontologists are an industrious
lot; we have faults aplenty, but laziness in the field is not among them.
We do love to find fossils; this is why most of us entered the profession
in the first place. We didn't scrutinize every inch of sediment for the
most basic of all scientific reasons. Life is short and the world is immense;
you can't spend your career on a single cliff face. The essence of science
is intelligent sampling, not sitting in a single place and trying to get
every last one. Under Darwinian gradualism, intelligent sampling followed
the usual handful-from-the-haystack method. The results obtained matched
the expectations of theory, and conceptual satisfaction (in retrospect,
one might say "sloth") set in. No impetus existed for the much
more laborious dismember-the-entire-haystack method, a quite unusual approach
in science. We could have worked this way, but we didn't because we had
no reason to do so. The Alvarez theory made this unusual approach necessary.
It forced us to look in a different way. "All observation must be
for or against some view if it is to be of any service!"
Consider two premier examples--the best-known marine terrestrial
groups to disappear in the Cretaceous-Tertiary extinction: ammonites and
dinosaurs. Both had been prominently cited as support for gradual extinction
toward the boundary. In each case, the Alvarez hypothesis inspired a closer
look via the dismember-the-haystack method, and in each case, this greater
scrutiny yielded evidence of persistence to the boundary and potentially
catastrophic death.
Ammonites are cephalopods (mollusks classified in the same group as
squids and octopuses) with coiled external shells closely resembling those
of their nearest living relative, the chambered nautilus. They were a
prominent, and often dominant, group of marine predators, and their beautiful
fossil shells have always been prized by collectors. They arose in mid-Paleozoic
times and had nearly become extinct twice before--in two other mass
dyings at the end of the Permian and of the Triassic periods. But a lineage
or two had scraped by each time. At the Cretaceous-Tertiary boundary,
however, all lineages succumbed, and to cite Wordsworth from another context,
there "passed away a glory from the earth."
My friend and colleague Peter Ward, paleontologist from the University
of Washington, is one of the world's experts on ammonite extinction; a
vigorous, committed man who adores fieldwork and could never be accused
of laziness on the outcrop. Peter didn't care much for Alvarez at first,
largely because his ammonites seemed to peter out and disappear entirely
some thirty feet below the boundary at his favorite site, the cliffs of
Zumaya on the Bay of Biscay in Spain. In 1983, Peter wrote an article
for Scientific American entitled "The Extinction of the Ammonites."
He stated his opposition to the Alvarez theory, then so new and controversial,
at least as an explanation for the death of ammonites:
The fossil record suggests, however, that the extinction of the ammonites
was a consequence not of this catastrophe but of sweeping changes in the
late Cretaceous marine ecosystem. . . . Studies of the fossils from the
stratigraphic sections at Zumaya in Spain suggest they became extinct
long before the proposed impact of the meteoritic body.
But Peter, as one of the smartest and most honorable men I know, also
acknowledged the limits of such "negative evidence." A conclusion
based on not finding something has the great virtue of unambiguous
potential refutation. Peter wrote: "This evidence is negative and
could be overturned by the finding of a single new ammonite specimen."
Without the impact hypothesis, Peter would have had no impetus to search
these upper thirty feet of section with any more care. Extinctions were
supposed to be gradual, and thirty feet of missing ammonites made perfect
sense, so why look any further. But the impact hypothesis, with its clear
prediction of ammonite survival right up to the boundary itself, demanded
more intense scrutiny of the thirty-foot haystack. In 1986, Peter was
still touting sequential disappearance: "Ammonites. . .appear to
have become extinct in this basin well before the K/T [Cretaceous-Teritary]
boundary, supporting a more gradualistic view of the K/T extinctions"
(Palaios, vol. 1, pp. 87-92).
But Peter and his field partners, inspired by Alvarez (if only by a
hope of disproving the impact hypothesis), worked on through the haystack:"The
remaining part of the Cretaceous section was well exposed and vigorously
searched and quarried." Finally, later in 1986, they found a single
specimen just three feet below the boundary. It was crushed, and they
couldn't tell for certain whether it was an ammonite or a nautiloid, but
this specimen did proclaim a need for even more careful search. (Since
nautiloids obviously survived the extinction--the chambered nautilus
still lives today--such a fossil right at the boundary would occasion
no surprise.)
Peter started a much more intense search in 1987, and the ammonites began
to turn up--mostly lousy specimens and very rare, but clearly present
right up to
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