Donald R Prothero

Department of Geology, Occidental College, Los Angeles, CA 90041, USA

The great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact.

Thomas Henry Huxley

For every problem, there is a solution that is simple, neat, and wrong.

H.L. Mencken

Abstract For the past 28 years, the trendy "bandwagon" in the geosciences has attempted to explain most mass extinctions by extraterrestrial impact events. However, the past decade of research has shown no significant evidence of impacts at any mass extinction horizon except for the Cretaceous-Tertiary boundary at 65 Ma. In fact, numerous paleontologists have even questioned whether the Cretaceous-Tertiary impact was as important as once supposed. Alleged impact horizons at the other major mass extinctions have proven to be of the wrong age or the wrong size. By contrast, there were many major impacts (especially in the late Eocene) that had no effect on life whatsoever, further falsifying the impact hypothesis as a general explanation. Explaining all the major mass extinctions by huge mantle-derived flood basalt eruptions has also failed, as such eruptions occur at only three of the extinction horizons. Attempts to find a general explanation that explains all mass extinctions are usually unsuccessful, because there are no common signals at every mass extinction. Each event shows a distinct and different pattern. Currently, the trendy model postulates high carbon dioxide and low oxygen in the atmosphere, although it only works for the Permo-Triassic, Triassic-Jurassic, and possibly Paleocene-Eocene events, and no others, and it has not fared well in preliminary testing.

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