there was limestone with more forams, but these belonged to only a
handful of species, all of them very tiny and all totally different from the
larger ones below.
Foraminifera come in distinctive, sometimes whimsical-seeming shapes.
Alvarez had been schooled in, to use his phrase, a “kind of hard-core
uniformitarianism.” He’d been trained to believe, after Lyell and Darwin,
that the disappearance of any group of organisms had to be a gradual
process, with one species slowly dying out, then another, then a third,
and so on. Looking at the sequence in the Gubbio limestone, though, he
saw something different. The many species of forams in the lower layer
seemed to disappear suddenly and all more or less at the same time; the
whole process, Alvarez would later recall, certainly “looked very abrupt.”
Then there was the odd matter of timing. The king-sized forams appeared
to vanish right around the point the last of the dinosaurs were known to
have died off. This struck Alvarez as more than just a coincidence. He
thought it would be interesting to know exactly how much time that half-
inch of clay represented.
In 1977, Alvarez got a job at Berkeley, where his father, Luis, was still
working, and he brought with him to California his samples from Gubbio.