The Sixth Extinction: An Unnatural History

gap, Lyell concluded that the unaccounted-for interval must have been a
long one, roughly equivalent to all the time that had passed since the
record had resumed. Using today’s dating methods, the lacuna he was
positing amounts to some sixty-five million years.
Darwin, too, was well informed about the discontinuity at the end of
the Cretaceous. In the Origin, he observed that the disappearance of the
ammonites seemed to be “wonderfully sudden.” And, just like Lyell, he
dismissed the ammonites and what they seemed to be saying. “For my
part,” he observed,
I look at the natural geological record, as a history of the world imperfectly kept, and
written in a changing dialect; of this history we possess the last volume alone, relating only
to two or three countries. Of this volume, only here and there a short chapter has been
preserved; and of each page, only here and there a few lines.
The fragmentary nature of the record meant that the semblance of
abrupt change was just that: “With respect to the apparently sudden
extermination of whole families or orders,” it must be remembered, he
wrote, that “wide intervals of time” were probably unaccounted for. Had
the evidence of these intervals not been lost, it would have shown “much
slow extermination.” In this way, Darwin continued the Lyellian project of
turning the geologic evidence on its head. “So profound is our ignorance,
and so high our presumption, that we marvel when we hear of the
extinction of an organic being; and as we do not see the cause, we invoke
cataclysms to desolate the world!” he declared.
Darwin’s successors inherited the “much slow extermination”
problem. The uniformitarian view precluded sudden or sweeping change
of any kind. But the more that was learned about the fossil record, the
more difficult it was to maintain that an entire age, spanning tens of
millions of years, had somehow or other gone missing. This growing
tension led to a series of increasingly tortured explanations. Perhaps
there had been some sort of “crisis” at the close of the Cretaceous, but it
had to have been a very slow crisis. Maybe the losses at the end of the
period did constitute a “mass extinction.” But mass extinctions were not