Marine animal extinction events have occurred episodically over the past 550 million years with expansive marine anoxia as the proximate kill mechanism. New evidence from a carbonate section in South China (Long’an) shows that the Late Devonian Hangenberg event should be counted as one such events. Postdoc Feifei Zhang have analyzed uranium isotopes in a marine succession and documented a signal that can be ascribed to a global change in ocean chemistry. The study is now published in Earth and Planetary Science Letters.

Vegetation in drier upland areas is thought to have first emerged on Earth with the evolution of seed plants around the time of the Hangenberg crisis 355 Ma. Photo credit: D. Bly NPS. Coronado National Park, AZ, USA.

Algeo, Scheckler and Maynars 2001 hypothesized that the event was linked to an increase in terrestrial plant cover, leading to increased nutrient supply in rivers. This may have led to eutrophication of semi-restricted epicontinental seas and could have stimulated algal blooms and caused marine anoxia. The new data supports this idea.