The Sixth Extinction: An Unnatural History

one, which appeared in the Proceedings of the National Academy of Sciences,
was by a pair of herpetologists. It was titled “Are We in the Midst of the
Sixth Mass Extinction? A View from the World of Amphibians.” The
authors, David Wake, of the University of California-Berkeley, and Vance
Vredenburg, of San Francisco State, noted that there “have been five
great mass extinctions during the history of life on this planet.” These
extinctions they described as events that led to “a profound loss of
biodiversity.” The first took place during the late Ordovician period, some
450 million years ago, when living things were still mainly confined to the
water. The most devastating took place at the end of the Permian period,
some 250 million years ago, and it came perilously close to emptying the
earth out altogether. (This event is sometimes referred to as “the mother
of mass extinctions” or “the great dying.”) The most recent—and famous
—mass extinction came at the close of the Cretaceous period; it wiped out,
in addition to the dinosaurs, the plesiosaurs, the mosasaurs, the
ammonites, and the pterosaurs. Wake and Vredenburg argued that, based
on extinction rates among amphibians, an event of a similarly
catastrophic nature was currently under way. Their article was illustrated
with just one photograph, of about a dozen mountain yellow-legged frogs
—all dead—lying bloated and belly-up on some rocks.