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"After duly eliminating the insect eggs and giving due credit to Walter in
our subsequent scientific publications," Dr. Officer said, "we found that all
the solid spherules, throughout the whole section, extended above and
below the terminal Cretaceous layer. They were present in sediments
spanning a time period of several million years and could therefore not
have come from impact." 4 6
As research continued, the spherules turned up at over 60 K-T
sites. Those found outside the United States were solid, rich in
nickel and iron, and often composed of spinel. Some of the spinels
have iridium concentrations of up to 500 ppt. These spinels are not
a dispersed chemical element like iridium, which for all we know
can be dissolved and reprecipitated, and whose exact source in the
boundary clay is not known to this day, but rather are physical
objects—spherules up to 100 microns (1 micron = 10~ 6 m) in diam-
eter. Once locked into a sediment, these spherules would be difficult
to move and thus they help to decide whether the strange features
of the boundary clay—iridium, shocked quartz, spherules—were
originally present in a peak or in a hill. A group of French geologists
found that at El Kef, Morocco, and at several other K-T sites, iridium
spreads over a broad hill, but the spinels occur in a razor-sharp peak
right at the boundary. 4 7 They concluded that the spinels (and thus
the boundary clay) took less than 100 years to deposit—a blink of
the eye in geologic time.
C HALLENGE
M ET
Officer and Drake succeeded neither in their effort to falsify impact
by showing that the K-T event was not instantaneous (arguments 1 a
and lb) nor in their attempt to discredit the evidence for impact
(argument 2). In the process, though, scientists learned a great deal,
especially about the geochemistry of iridium. Certainly the efforts of
the doubters failed to discourage the proponents, who were growing
in number. But on the other hand, those who supported the theory
were equally unable to sway its firmest opponents. In fact, only a
vanishingly small number are on record as ever having changed their
minds on the Alvarez theory. One need read only a fraction of the
vast literature on impact to predict with near certainty which side a
given author will take in all subsequent papers: the same as in previ-
ous ones. Glen notes that he has "found neither in planetary geology
nor in impacting studies anyone who ever wavered from the impact-
as-extinction-cause component of the hypothesis, nor in vertebrate
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