Evolutionary Catastrophes is an exploration of the role of catastrophes in mass extinctions. It is a compact and tautly written volume, into which Courtillot fits explanation of basic science, description of recent discoveries and controversies, and even some historical background — while maintaining a lively, almost chatty, tone. The result is popular science writing of the best kind, a real delight for anyone interested in geology or evolutionary history.

Courtillot begins with an introduction to paleontology and mass extinctions, touching on the problems of stratigraphy and the history of uniformitarian-catastrophism debates. He then introduces the widely popularised meteorite impact explanation for the Cretaceous-Tertiary extinction, in a historical account that starts with the Alvarezes' discovery of an iridium anomaly and follows the steady accumulation of evidence.

But the core of Evolutionary Catastrophes is an alternative explanation for this and other great mass extinctions: cataclysmic volcanism. Courtillot starts with an introduction to paleomagnetism, his own field, and an account of how he became involved with the Deccan Traps, a huge expanse of lava flows in India. These date to the Cretaceous-Tertiary boundary and the observed effects of volcanism on climate suggest an obvious causal mechanism for the extinction event. Taking a broader sample reveals a compelling correlation of traps with extinction events: there are as many as seven matches, including most notably one between the Siberian Traps and the great Permian-Triassic extinction. Traps generally are found at the old ends of volcano chains and are connected with continental breakup and the origins of hot spots. Intriguing mantle dynamics (possibly reaching down to the core) are involved in the plumes that create traps and underlie hot spots — and there may be a connection with reversals of the Earth's magnetic field.

Returning to the impact theory, Courtillot describes the hunt for the crater, the discovery of a candidate at Chicxulub, and the ongoing debates. Evidence suggests that the Chicxulub impact was contemporaneous with the Deccan Traps — and when it comes to explaining extinction events, Courtillot sums up the score as "meteorites, one; traps, seven", suggesting the meteorite impact may have been a grand coincidence. In the final chapter he takes a quick glance at anthropogenic extinctions and climate change, the role of catastrophes in shaping broad evolutionary patterns, and the past and future of the geosciences.

October 1999

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