Geoscience Reference
In-Depth Information
The question of the effect of impact on life is surely important,
for if the collision that left the Chicxulub crater behind did
not
cause the extinction of the 70 percent of species that perished at the
end of the Cretaceous, the Alvarez theory would remain merely a
scientific curiosity. Yes, objects from space do strike the earth now
and then, but even one the size of a large mountain does little harm
to life (or to geological orthodoxy). If on the other hand, impact did
cause the extinction, then paleontology, geology, and biology would
never be the same. Our conception of the role of chance in the cos-
mos, our view of life and its evolution, our understanding of our
own place—each would be irrevocably altered.
The Alvarez team left no doubt that they believed that the
impact caused the mass extinction. They might have called their
1980 article in
Science
"Evidence for Impact at the Cretaceous-
Tertiary Boundary" and waited until the case for impact was strongly
corroborated before going on to connect it to mass extinction.
Instead they gave it the provocative title, "Extraterrestrial Cause for
the Cretaceous-Tertiary Mass Extinction" and set out to show both
that impact had occurred
and
that it had caused the K-T mass
extinction.
The original paper was unusually long for
Science,
indicating that
Luis's Berkeley protege from long ago, editor Philip Abelson, under-
stood that the new theory might be of more interest than most.
However, almost all of the article's 13 pages were devoted to describ-
ing the iridium measurements and other chemical tests; the bio-
logical consequences of impact covered only half a page. This was
undoubtedly because the Alvarez team, though long on scientific tal-
ent, was demonstrably short on knowledge of paleontology. Luis was
a physicist; Asaro and Michel were chemists; Walter was a geologist,
but not a paleontologist. In retrospect, since they did not have pale-
ontological credentials, it was both proper and good strategy for the
Alvarezes to introduce their theory but to leave to others the task of
testing it against the facts. Walter knew that Wegener's theory of con-
tinental drift had languished for decades in part because in seeking a
mechanism to explain why the continents had drifted, he strayed
outside his field into the territory of the geophysicists, who immedi-
ately pronounced drift impossible, thus putting an end to the matter
for half a century.
For the first few years after its appearance, paleontologists did
not believe that they needed to take the Alvarez proposal seriously.
Even if impact were strongly corroborated—even if the crater were
found—that would not necessarily mean that the impact had caused
the mass extinction. More importantly, paleontologists believed that
