Scientists have uncovered new evidence that a lethal pulse of UV radiation from the Sun may have played an important role in the Earth’s biggest mass extinction event that shook the planet about 250 million years ago.
The study, published earlier this month in the journal Science Advances, found that pollen preserved in 250 million-year-old rocks contain compounds that function like sunscreen which plants likely produced to protect themselves from the harmful ultraviolet (UV-B) radiation.
Previous studies have shown that during this time period, the planet underwent the end-Permian mass extinction event – the most severe of the big five mass extinction events that resulted in the loss of more than 80 per cent of Earth’s marine and terrestrial species.
In the latest research, scientists, including those from the University of Nottingham in the UK, developed a new method to detect plant sunscreen-like compounds in fossil pollen grains.
Earlier research has suggested that the catastrophic loss of biodiversity in this mass extinction event was a response to a palaeoclimate emergency that was triggered by a continental-scale volcanic eruption that covers much of modern-day Siberia.
Studies have suggested that about 80 per cent of marine species that went extinct during the event died due to water acidification from intense volcanic activity.
However, researchers could not accurately quantify how terrestrial life was particularly killed by volcanically triggered mechanisms.
Scientists have previously noted following decades of research that the volcanic activity during this event drove the release of massive amounts of carbon into the atmosphere that had been locked up in Earth’s interior, which caused large-scale greenhouse warming.
Research had also suggested that this global warming event was accompanied by a collapse in the Earth’s ozone layer.
Now, scientists have found support for this theory from the abundant occurrence of malformed spores and pollen grains which indicate that the planet experienced an influx of mutagenic UV irradiation.
“Plants require sunlight for photosynthesis but need to protect themselves and particularly their pollen against the harmful effects of UV-B radiation,” study author Barry Lomax from the University of Nottingham said in a statement.
“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,” Dr Lomax explained.
In the new study, researchers developed a method to detect these compounds in fossil pollen grains recovered from Tibet.
They detected much higher concentrations of these “phenolic compounds” in these grains that were produced during the mass extinction, at the peak phase of volcanic activity.
Such elevated levels of UV-B radiation may have had even further-reaching and longer-lasting impacts on the entire Earth, researchers said.
Citing recent studies, they say elevated UV-B stress can reduce plant biomass and terrestrial carbon storage that could have exacerbated the global warming of this time period.
“Enhanced UV-B flux at the Earth’s surface is expected to trigger cascading effects through the biosphere, with broader impacts on the carbon cycle and climate system,” researchers wrote.
The increased concentration of phenolic compounds may have also made plants less easily digestible, scientists say, adding that it could have made a hostile environment even more challenging for plant-eating animals.
“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,” Wes Fraser, another author of the study, added.
