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Great dyings wiped out vast numbers of species five times in the past 500
million years. Palaeontological detectives have a clear suspect in only one
case, an asteroid that hit the earth 65 million years ago, when the dinosaurs
died at the end of the Cretaceous. In The Late Devonian Mass Extinction
(Columbia University Press, $20, ISBN 0 231 07505 7), George R. McGhee
marshals evidence that a series of impacts caused the late Devonian mass
extinction 367 million years ago. The case is not as clear as at the end of
the Cretaceous, but it does merit a serious hearing.