About 252 million years ago, 96% of all species on planet Earth disappeared in what is known as the Permian-Triassic mass extinction or Permian extinction, the third great extinction on planet Earth, and also the largest in its entire history. .
At this stage, there were large reptiles such as sputosaurs, distant relatives of turtles, and gorgonians.
Scientists have known for years that those responsible for the disappearance of more than 70% of animal species and 90% of marine life were the Siberian eruptions of volcanoes, which ravaged the entire planet, throughout the world. Gondwana supercontinent; in addition to acid rain, which had a local effect.
Now, a recent investigation suggests that, in parallel, there must have been a serious decrease in the thickness of the ozone layer , which contributed to further aggravate the global crisis.
The ozone layer is what allows life to exist on Earth, absorbing harmful radiation from the Sun, and not only under the oceans, where organisms are protected from deadly radiation, particularly UV-B wavelengths. , which cause mutations in DNA.
To corroborate this, the scientists carried out an experiment to check the effect of high UV radiation on conifers and other types of trees.
The team of researchers irradiated high doses of UV-B on the plants, up to 13 times stronger than on Earth today , simulating the effects of the depletion of the ozone layer caused by the huge volcanic eruptions that must have occurred at the end of the Permian Period.
During the two-month experiment, none of the trees died, but all the seed cones, or pine cones, withered within days of emerging, leaving the trees sterile.
However, when they were re-exposed to natural light, the trees regained the ability to produce healthy seed cones in later years.
Therefore, the big problem and the reason why the extinction was so serious lies in this disruption in the life cycle. In other words, repeated episodes of sterility could have hampered population growth over time.
“Paleontologists have devised various death scenarios for mass extinctions, but plant life is not affected by dying suddenly as much as by interrupting a part of the life cycle, such as reproduction, over a long period of time, causing the population dwindles and potentially disappears, “according to co-author Cindy Looy, associate professor of integrative biology at the University of California at Berkeley.
“If you repeatedly disrupt several of the world’s dominant plant lineages, you could set off trophic cascades by destabilizing the base of the food web, which doesn’t work very well for land animals,” he added.
On the way to the sixth mass extinction
The effect of high UV radiation on conifers and potentially other trees not only gives clues about what happened 250 million years ago; It also suggests caution today in the introduction of chemicals that deplete the Earth’s ozone layer , which has not yet recovered after a global ban on chlorofluorocarbon refrigerants in the 1980s; in fact, it will not be easy for him to recover.
In fact, the findings not only communicate about past extinctions, but also about Earth’s future prospects as climate change, habitat destruction and pollution prepare us for the sixth mass extinction.
Reference: JP Benca el al., “UV-B – induced forest sterility: Implications of ozone shield failure in Earth’s largest extinction,” Science Advances (2018). advances.sciencemag.org/content/4/2/e1700618
