University of Calgary

Permian mass extinction not linked to lack of oxygen in ocean, study reveals

UToday HomeJuly 17, 2013

The latest Permian extinction that took place approximately 252 million years ago was the most severe in Earth’s history and led to the loss of more than 90 per cent of marine life.

Until now, it was believed that the main driver for the extinction was linked to the loss of oxygen in global oceans. But a team of University of Calgary researchers from the departments of Geoscience and Physics and Astronomy recently discovered — contrary to common belief — that the ocean shelf environment actually remained under oxygenated conditions during the latest Permian mass extinction.

Their research raises anew the question: If lack of oxygen didn’t kill life, what did?

How mass spectrometry helped uncover prehistoric truth

The study, which involved the examination of rock records in the Canadian High Arctic, was co-authored by Bernadette Proemse, postdoctoral fellow in geoscience; Stephen Grasby, adjunct professor and geochemist at the Geological Survey of Canada; Michael Wieser, associate professor in physics and astronomy; and Bernhard Mayer and Benoit Beauchamp, geoscience professors.

By relying on novel techniques (molybdenum stable isotopes), the university team was able to assess changes in ocean oxygen across the extinction boundary.

“It took us three years to optimize the technique to produce reliable, reproducible results at high precision and accuracy,” says Proemse. “This is extremely crucial for this type of analysis because molybdenum is a trace metal and concentrations in the samples are therefore very low. Advances in the analytical techniques in the field of mass spectrometry have enabled us to analyze trace metals and their isotopes and to look at new geochemical tools and tracers that could not be studied before,” she adds.

Finding proves oxygen existed during mass extinction

The combination of geologic knowledge, geochemistry expertise, cutting-edge analytical equipment, and long-long hours of data gathering, confirmed that the ocean shelf environment in that region remained under oxic conditions during the mass extinction.

“Our study proves that even under well oxygenated conditions, there was still a massive loss of life,” explains Grasby. “Although there are some areas that clearly did become anoxic during the extinction, it was not a loss of oxygen that killed most life on the planet. In fact, our research shows that there remained large areas of well oxygenated waters. Consequently, it still remains unclear what did kill most life at that time,” he concludes.

The complete study was published in the Journal Geology.

 Bernadette Proemse, postdoctoral fellow in the Department of Geoscience, lists isotope geochemistry and Arctic research among her research interests. Here, Proemse is on the shore of Ellesmere Island. Photo by Stephen GrasbyBernadette Proemse, postdoctoral fellow in the Department of Geoscience, is an expert in isotope geochemistry and Arctic research. Here, Proemse is on the shore of Ellesmere Island. Photo by Stephen Grasby
 Stephen Grasby stands on the rock layer that marks the worst extinction in earth history, as exposed as the West Blind Fiord exposure, Ellesmere Island. Shales above this are devoid of any signs of life, but show geochemical evidence for being deposited iStephen Grasby stands on the rock layer that marks the worst extinction in earth history, as exposed as the West Blind Fiord exposure, Ellesmere Island. Shales above this are devoid of any signs of life, but show geochemical evidence for being deposited in a well oxidized ocean. Photo by Robert Pappalardo
 View to the east looking over Buchanan Lake on Axel Heiberg Island. Ellesemere Island is in the background. Samples were collected from gullies near the lake on the centre right of the photograph. Photo by Stephen GrasbyView to the east looking over Buchanan Lake on Axel Heiberg Island. Ellesemere Island is in the background. Samples were collected from gullies near the lake on the centre right of the photograph. Photo by Stephen Grasby
 Photograph of shale deposited during the worst extinction event in Earth history, as exposed at the Buchanan Lake section. This deeper water environment shows that the ocean waters were strongly anoxic, to the extent that hydrogen sulphide gas was formedPhotograph of shale deposited during the worst extinction event in Earth history, as exposed at the Buchanan Lake section. This deeper water environment shows that the ocean waters were strongly anoxic, to the extent that hydrogen sulphide gas was formed in the water column, leading to precipitation of the iron sulphide mineral pyrite (bright gold bands). Photo by Stephen Grasby

 

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