Geoscience Reference
In-Depth Information
warned that "The magnetic zones recorded in these terrestrial sec-
tions in Alberta, Montana, and New Mexico cannot be securely cor-
related with the magnetic polarity time scale."
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Officer and Drake had offered evidence from three geologic sec-
tions that they claimed showed that the K-T event took place at dif-
ferent times around the world and therefore could not have been the
result of an instantaneous global catastrophe, which if true would
falsify the Alvarez theory (argument la). When the original papers
that they cited were reviewed in detail, however, their claimed evi-
dence was found either to be nonexistent or to be in serious doubt.
(Later work confirmed that Officer and Drake were indeed wrong:
Wherever it has been studied, the K-T boundary falls firmly within
Chron 29R.)
In a 1984 paper, Walter and Luis Alvarez, Asaro, and Michel had
the last word: "A review by scientists who have not been active in
the field might have been valuable if it had been balanced, but
unfortunately, Officer and Drake use a double standard, in which
they apply keen scrutiny to evidence favoring the impact theory—
as, of course, they should—but uncritically accept any results, no
matter how flawed, that contradict it. They fail to mention most of
the data that support the theory. Instead, they fix their attention on
a few cases that can be made to look like contradictions."
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The title of Officer and Drake's 1983 paper in
Science,
"The
Cretaceous-Tertiary Transition," conveyed the message of their argu-
ment lb, showing that the change from the one geologic period to
the other had not been sudden, much less instantaneous. In their
view, there had been instead a finite "transition," a gradual shift, con-
sistent with uniformitarianism. Under the impact scenario, the time
taken by the transition "should be zero," they argued, and if the
fossils on one side of the boundary had been gradually replaced
by those on the other, rather than disappearing suddenly right at
the K-T boundary, the event could not have been instantaneous. But
as we will see, the fossil record can be hard to read. Fossil-bearing
sediments, after being deposited initially, can be stirred by waves and
redeposited, upsetting the original stratigraphy in a process called
re-
working.
Burrowing organisms carry material from one stratigraphic
level to another, mixing up the sedimentary and fossil record and
making once sharp peaks appear gradual (bioturbation). Officer and
Drake did acknowledge this difficulty, writing, "Bioturbation is an
important process affecting marine sedimentary sequences and can
blur or obscure transition events," but never again in their paper
did they refer to the process as having any actual effect.
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Thus they
