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laminations that would have been destroyed by bioturbation, allow-
ing that effect to be ruled out in this case.
Over the years, Huber and his colleagues have conducted de-
tailed studies of the core from ODP Site 738.
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7
They have found
that specimens of some foram species that are known to have gone
extinct at the K-T boundary, and of specimens of inoceramids, a
group of clamlike creatures that became extinct well below the
boundary, occur in the core far above the boundary, where they
could have gotten only by reworking. Thus, in this core, contrary to
the claims of MacLeod and Keller, reworking is prominent. This
point is further supported by studies of strontium and carbon iso-
tope ratios within the core. Huber concludes that "the high occur-
rences of Cretaceous species in lower Paleocene [lowest Tertiary]
sediments are likely the result of extensive reworking."
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8
He be-
lieves that only two of the Cretaceous species in the core from ODP
Site 738 survived the K-T boundary and that the rest are reworked.
But if MacLeod and Keller's methods for detecting reworking can
err in this most studied of deep-sea cores, how do we know they are
not in error in the other cores and geologic sections that they have
studied and pronounced free of reworking? The two of them appear
to be almost alone among micropaleontologists in denying that the
foram evidence corroborates the impact-extinction link. But let us
remind ourselves that we are not trying to prove that link, we are
asking whether the foram evidence falsifies prediction 2, that spe-
cies that became extinct at the K-T boundary will not be found
above the iridium horizon, except where reworked. The majority of
opinion is that the evidence does not.
What of prediction 1, that species will not have begun to go
extinct prior to the boundary and will have disappeared suddenly?
Keller, with MacLeod, continues the claim she made at Snowbird II
and repeatedly since: The foram extinctions started as early as
300,000 years before the K-T boundary. But once again we find
ourselves confronting the dreaded Signor-Lipps effect, which inex-
orably causes a sharp extinction to appear gradual, even at a modern
tidal flat, where all the "extinctions" took place in an instant. How
can it be ruled out in the case of the forams? Prediction 1 is not fal-
sified by the foram evidence.
T
HE
F
OSSILS
S
PEAK
The history of understanding the ammonite and fossil plant extinc-
tions at the K-T boundary shows how absent or negative evidence—
