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UV Radiation Contributed to Mass Extinction Event

Sun rays passing through a covering of trees.
Credit: Wonderlane on Unsplash.
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A new study of sunscreen-like chemicals detected in fossilized plants suggests ultraviolet (UV) radiation contributed to mass extinction events. The research is published in Science Advances.

Plant’s require protection against UV-B radiation

Recent studies have identified phenolic compounds in pollen, preserved in 250-million-year-old rock, that function like sunscreen. “Plants require sunlight for photosynthesis but need to protect themselves and particularly their pollen against the harmful effects of UV-B radiation,” says Professor Barry Lomax, chair in Plant Palaeobiology at the University of Nottingham. “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.”

Lomax is part of a collaborative team of scientists that created a new method for detecting such compounds. “We have developed a method to detect these phenolic compounds in fossil pollen grains recovered from Tibet, and detected much higher concentrations in those grains that were produced during the mass extinction and peak phase of volcanic activity,” says Professor Liu Feng from the Nanjing Institute of Geology and Palaeontology, who is the first author of the study. These data suggest that UV-B radiation likely contributed to the end-Permian mass extinction, which occurred 250 million years ago.

The end-Permian mass extinction

The end-Permian mass extinction was the most devastating of the 5 major extinction events in Earth's history, where approximately 80% of marine and terrestrial species were lost. The cataclysmic reduction in biodiversity was a subsequent effect of a continental-scale volcanic eruption. Huge amounts of carbon – once trapped in the Earth’s interior – were spewed into the atmosphere, triggering global warming. As the Earth’s temperature increased, a collapse in the ozone layer also likely occurred, the researchers suggest: “Our data reveal an excursion in UV-B-absorbing compounds (UACs) that coincide with a spike in mercury concentration and a negative carbon-isotope excursion in the latest Permian deposits, suggesting a close temporal link between large-scale volcanic eruptions, global carbon and mercury cycle perturbations and ozone layer disruption.”  

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Increased levels of UV-B can have wide-reaching and prolonged effects on the planet’s entire ecosystem. Modeling work has demonstrated that heightened UV-B exposure leads to a reduction in plant biomass and a decrease in carbon storage on land, exacerbating global warming. Plants exposed to higher levels of UV-B also produce more phenolic compounds, which make the tissue less digestible for herbivores, further impacting biodiversity. “Volcanism on such a cataclysmic scale impacts on all aspects of the Earth system, from direct chemical changes in the atmosphere, through changes in carbon sequestration rates, to reducing volume of nutritious food sources available for animals,” Dr. Wes Fraser, reader in physical geography at Oxford Brookes University and a co-author of the study concludes.

Reference: Liu F, Peng H, Marshall JEA, et al. Dying in the Sun: Direct evidence for elevated UV-B radiation at the end-Permian mass extinction. Sci Adv. 9(1):eabo6102. doi:10.1126/sciadv.abo6102.

This article is a rework of a press release issued by the University of Nottingham. Material has been edited for length and content.