WALTER Alvarez came from a long line of distinguished scientists. His
great-grandfather and grandfather were both noted physicians, and his
father, Luis, was a physicist at the University of California-Berkeley. But it
was his mother who took him for long walks in the Berkeley hills and got
him interested in geology. Walter attended graduate school at Princeton,
then went to work for the oil industry. (He was living in Libya when
Muammar Gaddafi took over the country in 1969.) A few years later he got
a research post at the Lamont-Doherty Earth Observatory, across the
Hudson from Manhattan. At the time, what’s sometimes called the “plate
tectonics revolution” was sweeping through the profession, and just
about everyone at Lamont got swept up in it.
Alvarez decided to try to figure out how, on the basis of plate
tectonics, the Italian peninsula had come into being. Key to the project
was a kind of reddish limestone, known as the scaglia rosso, which can be
found, among other places, in the Gola del Bottaccione. The project
moved forward, got stuck, and shifted direction. “In science, sometimes
it’s better to be lucky than smart,” he would later say of these events.
Eventually, he found himself working in Gubbio with an Italian geologist
named Isabella Premoli Silva, who was an expert on foraminifera.
Foraminifera, or “forams” for short, are the tiny marine creatures
that create little calcite shells, or tests, which drift down to the ocean
floor once the animal inside has died. The tests have a distinctive shape,
which varies from species to species; some look (under magnification) like
beehives, others like braids or bubbles or clusters of grapes. Forams tend
to be widely distributed and abundantly preserved, and this makes them
extremely useful as index fossils: on the basis of which species of forams
are found in a given layer of rock, an expert like Silva can tell the rock’s
age. As they worked their way up the Gola del Bottaccione, Silva pointed
out to Alvarez a curious sequence. The limestone from the last stage of
the Cretaceous period contained diverse, abundant, and relatively large
forams, many as big as grains of sand. Directly above that, there was a
layer of clay about half an inch thick with no forams in it. Above the clay
tuis.
(Tuis.)
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