Analysis showed that pollen, dating back to the Permian-Triassic mass extinction about 250 million years ago, produced “sunscreen” compounds that protect against harmful ultraviolet radiation. Around 80 percent of all marine and land species disappeared in that time.

What happened?

For the study, published Jan. 6 in the journal Science Advances, an international team of scientists developed a new method of using a laser beam to study tiny particles. They “grow” inside the rocks of Southern Tibet.

Scientists say plants rely on photosynthesis to convert sunlight into energy, but they also need a mechanism to block harmful ultraviolet radiation.

Because UV-B is harmful to us, it is also harmful to plants. Plants can change their chemistry and produce their own equivalent versions of sunscreen compounds. Their chemical structure scatters the high-energy wavelengths of ultraviolet radiation and prevents pollen grains from penetrating into tissues.
– said Barry Lomax, co-author of the study and professor of plant paleobiology at the University of Nottingham in Great Britain.

In this case, the burst of radiation “did not kill the plants immediately, but rather slowed them down, reducing their ability to photosynthesize, causing them to become sterile over time.” In the end, extinction occurs not because the ultraviolet instantly fry the plants, but because of a lack of reproduction.

Experts have long The Permian-Triassic extinction was a response to a “paleoclimatic emergency”, caused by the eruption of the Siberian Traps, a major volcanic event on the territory of modern Siberia. The catastrophic event forced carbon clouds buried deep in the Earth’s bowels to rise into the stratosphere, leading to global warming, which researchers say “caused the destruction of Earth’s ozone layer.”

When you reduce the ozone layer, you get more UV rays,
– Adds Lomax.

In their study, the scientists also found a link between the increase in UV radiation and how this changes plant chemistry, leading to “loss of insect diversity.” The leaves contained less nitrogen and were no longer nutritious enough for the insects that ate them. Additionally, plant tissues became less palatable and less digestible for herbivores.