Two pulses of extinction during the Permian-Triassic crisis

The Permian-Triassic mass extinction is the most severe biotic crisis identified in Earth history. Over 90% of marine species were eliminated(1,2), causing the destruction of the marine ecosystem structure(3). This biotic crisis is generally interpreted as a single extinction event around 252.3 million years ago(2,4-6), and has been variously attributed to the eruption of the Siberian Traps or possibly a bolide impact(7-10). Here we demonstrate that the marine extinction consisted of two pulses, separated by a 180,000-year recovery phase. We evaluated the range of 537 species representing 17 marine groups in seven Chinese sections from a 450,000-year interval spanning the Permian-Triassic boundary. The first stage of extinction occurred during the latest Permian, and was marked by the extinction of 57% of species, namely all plankton and some benthic groups, including algae, rugose corals, and fusulinids. The second phase occurred in the earliest Triassic, and resulted in the extinction of 71% of the remaining species. This second extinction phase fundamentally altered the marine ecosystem structure that had existed for the previous 200 million years. Because the two pulses showed different extinction selectivity, we conclude that they may have had different environmental causes.