Newly-found chemicals in fossil plants reveal UV-B radiation caused Permian mass extinction

"We have developed a method to detect these phenolic compounds in fossil pollen grains."
Nergis Firtina
Fossilized leaf stock image.
Fossilized leaf stock image.

Dina Damotseva/iStock 

A new study demonstrates that pollen preserved in rocks that are 250 million years old has substances that act like sunscreen and are created by plants to shield them from damaging ultraviolet (UV-B) radiation. The evidence points to the importance of a UV-B pulse in the end-Permian mass extinction catastrophe.

According to the press release, Professor Liu Feng of the Nanjing Institute of Geology and Palaeontology is leading a team of researchers from the University of Nottingham, China, Germany, and the UK who have created a new technique to identify sunscreen-like plant chemicals in prehistoric pollen grains.

One of the most severe extinction

Occurred 250 million years ago, the Permian mass extinction is the most severe of the big five mass extinction events, with the loss of 80 percent of marine and terrestrial species. In reaction to a palaeoclimate emergency brought on by the eruption of a continental-scale volcano that covered much of present-day Siberia, there was a catastrophic loss of biodiversity.

Because of the large-scale greenhouse warming caused by the release of enormous amounts of carbon locked up in the Earth's interior into the atmosphere, a breach in the ozone layer on Earth coincided with this case of global warming. A breach in the ozone layer on Earth coincided with this case of global warming.

Newly-found chemicals in fossil plants reveal UV-B radiation caused Permian mass extinction
Alisporites tenuicorpus, the pollen grain used in the study.

"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," Professor Barry Lomax from the University of Nottingham explained.

"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," Liu Feng added.

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Longer-lasting impacts on the entire Earth System

Even more far-reaching and long-lasting effects on the entire Earth System may result from elevated UV-B levels. Increased UV-B exposure decreases plant biomass and land carbon storage, which would accelerate global warming, according to recent modeling studies. In addition to making plant tissue less easily digested due to the increased phenolic chemical concentration, this creates an even more unfriendly environment for herbivores.

"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 the volume of nutritious food sources available for animals," co-study author Dr. Des Fraser said.

The study was published in Science Advances on January 6.

Study abstract:

Land plants can adjust the concentration of protective ultraviolet B (UV-B)–absorbing compounds (UACs) in the outer wall of their reproductive propagules in response to ambient UV-B flux. To infer changes in UV-B radiation flux at Earth's surface during the end-Permian mass extinction, we analyze UAC abundances in ca. 800 pollen grains from an independently dated Permian-Triassic boundary section in Tibet. Our data reveal an excursion in 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. Because enhanced UV-B radiation can exacerbate the environmental deterioration induced by massive magmatism, ozone depletion is considered a compelling ecological driver for the terrestrial mass extinction.