Geoscience Reference
In-Depth Information
Luis Alvarez died on September 1, 1988, ending one of the most
versatile, successful, and combative careers in modern science. At
Snowbird II, held just six weeks later, one of the participants pro-
posed two minutes of silence in his honor. Walter rose to say, "My
father would have been mortified. He'd much rather have a good
fight in his memory."
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T
HEORIES
OF
D
INOSAUR
E
XTINCTION
If impact did not kill the dinosaurs, what did? Michael Benton, writ-
ing nearly three decades after Jepsen, found a total of about 65 seri-
ously proposed ideas.
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(He omits such recent suggestions as AIDS
and terminal constipation.) Taking a very coarse cut, Benton's list
can be aggregated as follows:
•
Medical problems ranging from slipped discs to disease.
• "Evolutionary drift into senescent overspecialization." (Some of
us may feel that we too are suffering from this malady—a sort of
reptilian chronic-fatigue syndrome.)
•
Competition with other animals, especially mammals.
• Floral changes: New plant species were unsuitable for dinosaurs
or poisoned them.
•
Climate change: too hot, too cold, too wet, too dry.
• Atmospheric change: high levels of oxygen, low levels of carbon
dioxide.
• Oceanic and topographic change: Seas retreated (we know that
during the late Cretaceous they did); or large volumes of fresh,
cold Arctic Ocean water spilled into the Atlantic, lowering
temperatures and causing drought.
• Volcanism, whose resulting soot and ash could have had the
same lethal effects as predicted for impact.
• Extraterrestrial events such as supernovae explosion and
meteorite impact.
Let us put these theories up against the criteria deduced by
David Raup from his career-long study of extinction: "For geograph-
ically widespread species, extinction is likely only if the killing stress
is one so rare as to be beyond the experience of the species, and thus
outside the reach of natural selection."
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But how widespread is
