A deadly pulse of ultraviolet (UV) radiation may have played a role in Earth’s largest mass extinction event, fossil pollen grains suggest.
The analysis found that pollen around the time of the Permian–Triassic mass extinction event, about 250 million years ago, produced “sunscreen” compounds that shielded against harmful UV-B radiation. At that time, about 80% of all marine and terrestrial species died out.
For the study, which was published Jan. 6 in the journal Science Advances (opens in new tab)A team of international scientists developed a new method of using laser beams to probe the tiny grains, which measure about half the width of a human hair and were found on rocks discovered in southern Tibet, according to a statement. were. (opens in new tab),
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Plants depend on photosynthesis to convert sunlight into energy, but they also need a mechanism to block harmful UV-B radiation.
“As UV-B is bad for us, it is equally bad for plants,” Barry Lomax (opens in new tab), co-author of the study and a professor of plant paleobiology at the University of Nottingham in the UK, told Live Science. “Instead of going [the pharmacy], plants can change their chemistry and make their own equivalent versions of sunscreen compounds. Their chemical structure serves to diffuse high-energy wavelengths of UV-B light and prevent it from penetrating inside the protected tissues of pollen grains.”
In this case, the radiation spike “did not kill the plants outright, but rather slowed them down by reducing their ability to photosynthesize, rendering them sterile over time,” Lomax said. “Then you wind up with extinction driven by a lack of sexual reproduction rather than UV-B frying the plants right away.”
Experts have long theorized that the Permian–Triassic extinction, classified as one of the five major extinction events on Earth, was in response to a “paleoclimate emergency” caused by the Siberian Traps eruption, which is now in modern times. There is a big volcanic event. Siberia. According to the researchers, the catastrophic event forced the accumulation of carbon buried deep in the stratosphere within Earth’s interior, resulting in a global warming event that “degraded Earth’s ozone layer”.
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“And when you thin the ozone layer, that’s when you end up with more UV-B,” Lomax said.
In their research, the scientists discovered a link between how the bursts of UV-B radiation changed the chemistry of plant tissues, which led to a “loss of insect diversity,” Lomax said.
“In this case, the plant tissue became less palatable and less digestible to the herbivore,” Lomax said.
Because plant leaves were low in nitrogen, they were not nutritious enough for the insects that ate them. This may explain why insect populations plummeted during this extinction event.
“Bugs often go out during mass extinction events, but that was not the case here,” Lomax said.