Geoscience Reference
In-Depth Information
Cretaceous and that something else caused the mass extinction; we
would be back at square one.
O
F
A
MMONITES,
P
LANTS,
AND
F
ORAMS
It is hard to think of four more diverse groups of organisms than the
ammonites, plants, and forams plus the dinosaurs. The ammonites
and forams both made their lives in the sea, but in completely dif-
ferent ways; both are fundamentally different from the plants. These
four have now been studied sufficiently to allow us to use them to
test the extinction half of the Alvarez theory.
AMMONITES
Ammonites were mollusks, like the squids and octopuses, that
ranged from about a centimeter to a meter in size. Their intricately
coiled and chambered shells provide some of our most beautiful fos-
sils. The ammonites first appeared in the mid-Paleozoic, survived
even the deadly end-Permian extinction, when 96 percent of all
species died, and expired at the end of the Cretaceous, 330 million
years after their arrival. Geologists, including Darwin (whose contri-
butions to that field earn him the title geologist) for over a century
had noted that the ammonite extinction marked the K-T boundary.
Yet when modern geologists took a closer look, they were not so
sure. Peter Ward of the University of Washington, a leading expert
on ammonites, tells of being invited to Berkeley in 1981, not long
after the Alvarez theory had appeared, to give a talk to assembled
Alvarezes and Berkeley paleontologists.
4
He told them of a theoret-
ical study he had just completed, which showed that the ammonites
should have gone extinct suddenly. This was music to the ears of the
Alvarezes, who lost no time in inviting Ward to dinner. According to
Ward, William Clemens, a Berkeley paleontologist whose office was
down the hall from Walter's and who was to become a bitter oppo-
nent of Luis's, left immediately after the talk without comment.
5
A
year later, after having done extensive ammonite collecting, Ward
returned to Berkeley to give another talk, this time announcing that
his new findings showed that the ammonites had apparently gone
extinct well below the boundary, thus contradicting prediction 1
and undercutting the Alvarez theory. This time Luis Alvarez stayed
away, while Clemens invited Ward to dine.
One of the best locations for finding ammonites near the K-T
boundary is in the Bay of Biscay off Spain, at its border with France,
where the relevant geologic section is well developed and well
