A new study has found that pollen grains preserved in rocks 250 million years old contain compounds that act as a sunscreen produced by plants to protect against harmful ultraviolet (UV-B) radiation.
The results show that a wave of ultraviolet-B (UV-B) radiation played an important role in ending the mass extinction during the Permian.
Scientists from the University of Nottingham in China, Germany and the UK, led by Professor Liu Feng of the Nanjing Institute of Geology and Paleontology, have developed a new method for detecting plant sunscreen compounds in fossil pollen.
Sunscreen-like chemicals found in ancient pollen grains indicate that ultraviolet radiation played a role in one of the largest mass extinctions that occurred 250 million years ago, according to findings published in Science Advances.
This mass extinction at the end of the Permian is the most severe of the five major mass extinctions, killing about 80% of marine and terrestrial species.
This catastrophic loss of biodiversity was a response to a climate catastrophe caused by a continental-scale volcanic eruption that engulfed much of present-day Siberia.
Volcanic activity released into the atmosphere a huge amount of carbon that was locked in the bowels of the Earth, which led to widespread global warming.
This global warming event was accompanied by the destruction of the Earth’s ozone layer. This theory is supported by a large number of deformed spores and pollen grains, indicating an influx of mutagenic ultraviolet radiation.
Professor Barry Lomax from the University of Nottingham explains: “Plants require sunlight for photosynthesis, but they must protect themselves and especially their pollen from the harmful effects of UVB radiation.
To do this, plants load the outer walls of pollen grains with compounds that act like sunscreen to protect vulnerable cells and ensure successful reproduction.”
Professor Liu Feng adds: “We developed a method for detecting these phenolic compounds in fossil pollen grains recovered from Tibet, and found much higher concentrations in those grains that formed during the mass extinction and the peak phase of volcanic activity.”
Elevated levels of UV-B radiation can have far-reaching and long-term effects on the entire Earth system.
Recent modeling studies have shown that higher UV-B pressure reduces plant biomass and terrestrial carbon stocks, exacerbating global warming.
The increased concentration of phenolic compounds also makes plant tissues less digestible, making harsh environments more difficult for herbivores.
Summarizing the team’s findings, Dr Wess Fraser of Oxford Brookes University commented: “The impact of volcanoes of this magnitude is catastrophic for all aspects of the earth system, from direct chemical changes in the atmosphere, through changes in the rate of carbon sequestration, to a reduction in available nutrient food sources for animals.”