UV radiation played a role in Earth's largest mass extinction

The end-Permian mass extinction from 250 million years ago is the most severe of the five mass extinctions our planet faced, decimating over 80 percent of marine and terrestrial plant and animal species. This catastrophic loss of biodiversity was triggered by the emplacement of a continental-scale volcanic eruption covering much of modern-day Siberia, which released massive amounts of carbon from the Earth’s interior into the atmosphere, generating a devastating global warming event that led to the collapse of the ozone layer.

Now, an international team of scientists has discovered that pollen preserved in rocks dating from that period contained compounds that function like sunscreen and were produced by plants to protect them from harmful ultraviolet radiation (UV-B). These findings suggest that a pulse of UV-B may have played an important role in the end-Permian mass extinction.

“Plants require sunlight for photosynthesis but need to protect themselves and particularly their pollen against the harmful effects of UV-B radiation. To do so, plants load the outer walls of pollen grains with compounds that function like sunscreen to protect the vulnerable cells to ensure successful reproduction,” explained Barry Lomax, a professor of Plant Paleobiology at the University of Nottingham.  

“We have developed a method to detect these phenolic compounds in fossil pollen grains (Alisporites-type) recovered from southern Tibet and detected much higher concentrations in those grains that were produced during the end-Permian mass extinction and peak phase of volcanic activity,” added Liu Feng, a paleontologist at the Nanjing Institute of Geology and Palaeontology.

The researchers discovered an increase in UV-B-absorbing compounds (UACs) which coincided with a massive rise in mercury concentration and a decrease in carbon isotopes in the latest Permian deposits, suggesting a close temporal link between large-scale volcanic eruptions, worldwide carbon- and mercury-cycle perturbations, and disruptions of the ozone layer. Thus, elevated UV-B levels most likely exerted far-reaching and long-lasting impacts on the entire planet, reducing plant biomass and terrestrial carbon storage and exacerbating global warming. Moreover, increased concentrations of phenolic compounds made plant tissue harder to digest, making an already hostile environment even more challenging for herbivores.

“Volcanism on such a cataclysmic scale influences all aspects of the Earth system, from direct chemical changes in the atmosphere, through changes in carbon sequestration rates, to reducing the volume of nutritious food sources available for animals,” concluded Wes Fraser, an expert in Organic Geochemistry at Oxford Brookes University.

The study is published in the journal Science Advances.   

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By Andrei Ionescu, Earth.com Staff Writer

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