The Geochemistry of Mass Extinction

The course of biological evolution is inextricably linked to that of the environment through an intricate network of feedbacks that span all scales of space and time. Disruptions to the environment have biological consequences, and vice versa. Fossils provide the prima facie evidence for biotic disruptions: catastrophic losses of global biodiversity at various times in the Phanerozoic. However, the forensic evidence for the causes and environmental consequences of these mass extinctions resides primarily in the geochemical composition of sedimentary rocks deposited during the extinction intervals. Thus, advancement in our understanding of mass extinctions requires detailed knowledge obtained from both paleontological and geochemical records. This chapter reviews the state of knowledge concerning the geochemistry of the 'big five' extinctions of the Phanerozoic: the Late Ordovician, the Late Devonian, the Permian-Triassic, the Triassic-Jurassic and the Cretaceous-Tertiary.