Since the Cambrian Explosion, ecosystems have suffered repeated mass extinctions, 5 of which wiped out half of all species: The Cretaceous–Paleogene extinction, the Triassic–Jurassic extinction, the Permian–Triassic extinction, the Late Devonian extinction and the Ordovician–Silurian extinction.

20 years ago, a sixth major extinction was put forth in the Middle Permian (262 million years ago) in China. This Capitanian extinction was known only from equatorial settings and it was not recognized as an actual global crisis and was instead considered just one of many lesser mass extinctions. David P.G. Bond and colleagues provide the first evidence for severe Middle Permian losses amongst brachiopods in northern paleolatitudes (Spitsbergen).

Their study says that the Boreal crisis coincided with an intensification of marine oxygen depletion, implicating this killer in the extinction scenario. The widespread loss of carbonates across the Boreal Realm also suggests a role for acidification. The new data cements the Middle Permian crisis's status as a true "mass extinction" in their minds, and advocate that the "Big 5" extinctions should now be considered the "Big 6."

Citation: David P.G. Bond et al., 'An abrupt extinction in the Middle Permian (Capitanian) of the Boreal Realm (Spitsbergen) and its link to anoxia and acidification', GSA Bulletin 14 Apr. 2015 DOI: 10.1130/B31216.1