Demolished Ozone Layer 252 Million Years Ago Left Trees Sterile From UV Radiation

Scientists recently tested how bonsai-like pine trees reacted to extreme ultraviolet radiation levels to reveal more about how a mass extinction 252 million years ago occurred. CHARLY TRIBALLEAU/AFP/Getty Images

Scientists are turning their eyes towards a curious new subject to better understand mass extinctions of Earth's history: a bonsai-like pine tree.

Like many investigations into the environment, scientists peek into the past in order to understand the future. In a new study, researchers from the University of California Berkeley have applied that idea to the bonsai tree in order to evaluate how plants react to high ultraviolet radiation—the same levels of radiation that may have occurred during the largest known mass extinction around 252 million years ago.

During the end of that period—called the Permian period—scientists hypothesize that species were wiped out after hundreds of thousands of years of Siberian volcanic eruptions destroyed the ozone layer. The loss of that protective layer, in part, led to the "Great Dying," which resulted in the loss of 70 percent of known land animals and 95 percent of marine life.

But, how exactly the lack of an ozone layer caused such a massive die-off isn't well understood. To find some answers, scientists in the lab of Cindy Looy, Berkeley integrative biology professor, tested bonsai-like pine trees, scientifically known as the Pinus mugo.

Dwarf pines in a growth chamber under simulated sunlight plus extra UV-B from two high-intensity lamps. Jeffrey Benca

"We came in and basically thought, okay, how could we actually test this—almost in a paleo-mythbusters type way," Jeffrey Benca, lead author and Berkeley graduate student, told Newsweek.

Benca used the plant growth chambers as a "time machine," as co-author and integrative biology professor at Berkeley, Ivo Duijnstee described it. He exposed 60 18-inch tall dwarf pine trees to ultraviolet-B radiation between 7.5 and 13 times stronger than Earth's typical UV-B levels. The findings, published Wednesday in Science Advances, revealed that after two months, 12 to 15 percent of pollen grains were misshapen in medium to high levels of radiation exposure. That frequency of misshapen pollen was at least four times higher than among those exposed to normal to low levels of radiation.

Normal and abnormal fossilized pollen from the Permian (top) and similar pollen from Pinus mugo in normal trees (bottom left) and those exposed to high levels of UV-B. Jeffrey Benca

The misshapen pollen indicates the trees were sterilized, at least temporarily. The pollen formed under the UV-exposed pine trees matched that of ancient pollen from the Permian period that was analyzed in previous studies. Another strange and unexpected result was that the seed cones (there are two different types of cones produced by conifer trees) were dying—even in shaded areas of the tree.

"These cones basically would open up, and before they would be receptive to being pollinated and fertilized, they perished," Benca said. "We basically ended up with these trees full of what we would call mummy cones."

This evidence suggests that during the mass extinction of the Permian period, sometimes called the Great Dying, some species of trees may have slowly died off, as a result of sterilization. This experiment—though just evaluating one, modern day species—offers one piece of the puzzle explaining what may have caused so many species to perish. For trees, so it seems, radiation may have dealt a lethal blow to plants' reproductive system.

Normal seed cones of the pine tree (left) compared to shriveled cones produced when the pines were irradiated with UV-B light. Jeffrey Benca

The present-day evidence of Benca's findings carries implications for future mass extinctions, particularly in regards to the state of the ozone layer, which protects Earth from harmful radiation.

That said, the ozone layer also offers a rare success story of humans repairing environmental damage over the past few decades. "It's actually one of the greatest international collaborations of different governments and different people looking at the science over time," Benca said.

Last November, the hole in the ozone layer was recorded at its record low. Earlier this month, evidence that the Montreal Protocol which banned the use of chemicals causing the hole was largely responsible for the improvements. A study back in 2009 revealed that without the Montreal Protocol to regulate ozone-depleting chemicals, DNA damage in the northern hemispheres mid-latitudes alone would have increased by 550 percent by 2065.

"We really dodged a bullet there that would have been catastrophic, not just for us, but for all ecosystems on the planet." Duijnstee said. The latest study, however, helps us understand what could have happened without the Montreal Protocol, and what likely happened millions of years ago.