Big 5 Mass Extinctions

Mass extinction events are considered to be: (1) biodiversity crises, determined primarily by significantly increased extinction rates, and (2) ecological (or biotic) crises, when the ecosystem consequences of the biospheric perturbation were disproportionately large when compared to the protracted/stepwise biodiversity loss alone. Only the end-Permian and end-Cretaceous mass extinctions were unequivocal mass extinctions sensu stricto. The end-Ordovician global event was only a major biodiversity crisis, whereas the Late Devonian and end-Triassic extinctions were major ecological (or biotic) crises. In the causal context, the end-Cretaceous catastrophe could have been caused by the impact of a giant meteorite, but most probably this was only a final step leading to the collapse of the biosphere, influenced earlier by Deccan trap volcanism. Four other mass extinctions are more (Mesozoic) or less (Paleozoic) certainly connected with Earth-bound destructive factors, with large igneous provinces as a leading proposed trigger. The volcanic greenhouse/icehouse scenario has been updated and is supported by recently discovered mercury anomalies. A wide spectrum of killing factors related to volcanic cataclysm, and augmented by non-volcanic factors, has operated within a totally different time scale. The concrete interrelationships and feedbacks were certainly specific for each of the mass extinctions, resulting in their inhomogeneity.