Death at the Cretaceous Tertiary boundary

Abstract

Abstract It is unusual in science for a major advance to be traceable to the publication of a single paper, but without question the study of mass extinctions received a huge stimulus, and considerable media interest, from the seminal paper in Science by Luis Alvarez, his son Walter and two nuclear chemist colleagues (Alvarez et al. 1980). Although phenomena from outer space had been invoked on a few previous occasions to account for mass extinctions, they were disregarded because of lack of evidence in support. This situation was changed radically with the discovery of a significant positive anomaly of the platinum-group trace metal iridium at the Cretaceous-Tertiary (K-T) boundary in Italy and elsewhere. This was held by Alvarez et al. to be most plausibly accounted for by the impact of an asteroid approximately 10 km in diameter. A few years later the impact hypothesis received strong support from an independent line of evidence, the presence of so-called shocked quartz at the K-T boundary in the North American Western Interior. Shocked quartz possesses distinctive multiple sets of lamellae which have only been recognised in rocks from well-established meteorite impact sites or at nuclear weapons test sites, and appears to signify the passage of shock waves under enormous pressures.