https://news.st-andrews.ac.uk/archive/great-dying-what-caused-earths-biggest-mass-extinction/
Monday 19 October 2020
New research led by the University of St Andrews and renowned German research centres helps answer one of the most asked questions in geoscience: what exactly caused the Earth’s biggest mass extinction?
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The team of researchers, led by Dr Hana Jurikova, now based at the University of St Andrews, used a novel analytical approach of different isotopes of the elements boron and carbon, retrieving the pH of the ancient ocean from fossil brachiopod shells. Although numerous brachiopod species also became extinct during the Great Dying, the team found brachiopod shells within the critical time interval which offered a snapshot of the rapid onset of the extinction. Seawater pH is a critical indicator that not only records ocean acidity, which varies depending on the amount of absorbed carbon dioxide (CO2), but together with carbon isotope constraints it also allowed the team to determine changes in the amount and sources of atmospheric CO2 at the time of the extinction event.
The team were able to determine that the trigger of the Permian-Triassic crisis was a large pulse of CO2 to the atmosphere originating from a massive flood basalt province, the result of a giant volcanic eruption in today’s Siberia. Analyses showed that the volcanisms released more than 100,000 billion tonnes of carbon into the atmosphere, triggering the onset of the extinction. This is more than 40 times the amount of all carbon available in modern fossil fuel reserves including carbon already burned since the industrial revolution.
The research team used innovative modelling to reconstruct the effect of such large CO2 release on global biogeochemical cycles and the marine environment. The findings showed that, initially, the CO2 perturbation led to extreme warming and acidification of the ocean that was lethal to many organisms, especially those building calcium carbonate shells and skeletons. The greenhouse effect, however, led to further dramatic changes in chemical weathering rates on land and nutrient input and cycling in the ocean that resulted in vast deoxygenation and probably also sulphide poisoning of the oceans, killing the remaining organism groups.
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https://doi.org/10.1038/s41561-020-00646-4
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