Geoscience Reference
In-Depth Information
FIGURE I O
Professor Charles
Officer. [Courtesy of H-O
Photographers.]
P
REEMPTIVE
S
TRIKE
If the Alvarez theory is correct, the change from Cretaceous time to
Tertiary time happened instantaneously, everywhere around the
globe, in which case the K-T boundary clay can represent but a mere
eyeblink of geologic time—a few hundred or a few thousand years at
most. Furthermore, the boundary would have to be the same age
everywhere. Officer and Drake claimed to have evidence that, on the
contrary, the age of the boundary differs by hundreds of thousands
of years at different locales. If the K-T boundary has one age at one
site and quite a different age at another, it obviously was not created
instantaneously and the impact theory is falsified. On the other
hand, without impact as its cause, the K-T boundary is likely to have
somewhat different ages at different locations around the globe. This
surprising fact has its roots in the way geology began.
As their understanding of the earth developed, early geologists
began to recognize that they could define distinctive rock units
that differed both from the older rocks below and the younger ones
above. More than a century ago, geologists began to give names to
these characteristic units that they could trace over wide distances:
Cambrian, Ordovician, Devonian, and so on. In this way the stan-
dard geologic column—the ideal sequence if all rock units were pre-
