A re-examination of the hypotheses for the Permian-Triassic Boundary extinction event

The biological crisis that occurred at the Permian-Triassic boundary represents the most extensive loss of species of any known event in the past ∼600 million years. Various models/hypotheses for the cause of this extinction event have been proposed, including bolide impact (1) and volcanism (2,3), and their effects; i.e. oceanic anoxia, oceanic overturn, excessive methane release, environmental change and even combi-nations of these possibilities (4,5). Massive volcanism (Deccan Traps) and/or bolide impact (Chicxulub) has been considered as the cause(s) of the end-Cretaceous extinc-tions. In this paper, a number of these models / hypotheses for the end-Permian will be discussed in terms of how they change the global carbon cycle; a measure of the severity/rapidity of an extinction event. In addition, new evidence for a major impact event at the end-Permian will be dis-cussed (1). The implication for yet another large impact event (Bedout) occurring con-temporaneously with extensive continental volcanism suggests that other severe mass extinction events that have occurred over the past∼600 million years require ‘multiple catastrophes’. The idea of multiple catastrophes was also applied to the current δ13