A fossil analysis showed that pollen preserved in 250-million-year-old rocks has substances that act like sunscreen, which plants create to shield them from damaging ultraviolet (UV-B) radiation. The evidence points to the role of UV-B radiation in the end-Permian mass extinction event.
The findings of the study, titled "Dying in the Sun: Direct evidence for elevated UV-B radiation at the end-Permian mass extinction" published in Science Advances, is the first direct proof that the ozone layer high in the atmosphere that protects life on Earth was primarily destroyed during that mass extinction.
The End-Permian Mass Extinction Event
The end-Permian mass extinction event that happened about 250 million years ago resulted in the extinction of 80% or more of marine and terrestrial species, which is the worst of the major five mass extinction events, Phys.org reports.
In reaction to a palaeoclimate emergency brought on by the eruption of a continental-scale volcano that covered most of present-day Siberia, there was a catastrophic loss of biodiversity.
Volcanic activity at that time released large-scale greenhouse gases, specifically enormous amounts of carbon trapped in the Earth's interior. It has been hypothesized that the collapse in the ozone layer on Earth coincided with this case of global warming event.
The prevalence of pollen grains and spores with abnormal shapes, which attest to an input of mutagenic UV radiation, lends support to this notion.
University of Nottingham Professor Barry Lomax explains that plants also have a protective mechanism against UV-B radiation's damaging effects on them and on their pollen. Plants do this by packing the outer walls of pollen grains with substances that act as sunscreen on the sensitive cells, safeguarding successful reproduction.
Researchers of the new study developed a technique to identify these phenolic chemicals in fossil pollen grains they recovered from Tibet. Professor Liu Feng noted that they were able to identify substantially larger quantities in those grains that were formed during the mass extinction and peak time of volcanic activity.
High Levels of UV-B Radiation Affected Plant Growth
According to a report by New Scientist, the team measured the concentrations of UV-absorbing compounds in fossilized pollen grains and spores from rocks in Tibet using a method called Fourier transform infrared microspectroscopy.
Study co-author Phil Jardine from the University of Münster in Germany said that the oldest rock strata were formed a few hundred thousand years prior to the extinction, and the youngest ones a few hundred thousand years after that.
According to him, since the sunscreen compounds should be preserved to a comparable degree throughout this rock sequence, the rise during the mass extinction must have been because plants were producing more of those substances. "This is the UV signal," Jardine said.
Increased UV exposure would have stunted the development of terrestrial plants, starving herbivores, and predators, and had a domino effect on ecosystems. Because water absorbs UV light, the effects on marine habitats would have been far less severe.
If nations had not decided in 1987 to phase out CFCs as part of the Montreal Protocol, the same process would be occurring once more today and would have worsened climate change.
Modeling studies suggest that there would have been severe ozone disturbance and collapse had it not been for the Montreal Protocol. Researchers noted that these kinds of agreements and environmental safeguards are crucial.
RELATED ARTICLE: 6th Mass Extinction Now Happening? Study Reveals Current Species Die-Off on Earth Caused by Humans
Check out more news and information on Climate Change in Science Times.
