The end-Permian mass extinction

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The largest known biotic crisis, removing on published estimates somewhere between roughly 80 and 96 per cent of marine species depending on the analysis and the method, and unusually severe on land as well — it is the only mass extinction known to have caused a major loss of insect families. Whole groups that had dominated Palaeozoic seafloors for two hundred million years, including the trilobites, disappear at or near this horizon. The dating from the Meishan reference section in Zhejiang is what makes the event tractable: uranium–lead ages on zircons from ash beds interbedded with the boundary limestone place the boundary at 251.902 ± 0.024 million years and constrain the main extinction pulse to roughly sixty thousand years. The Siberian Traps flood basalts are contemporaneous within the resolution of the dating, and the favoured mechanism is not the lava but the gases released when those magmas intruded coal, evaporite and carbonate sequences — carbon dioxide and methane driving warming, ocean anoxia and acidification. Recovery of ecosystem complexity took several million years, longer than after any other extinction.

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