Evidence of Fossil Pollen "Sunscreen" Links Mass Extinction to Ozone Layer Decline

Mass Extinction to Ozone Layer Decline

A group of scientists from China, Germany, and the UK led by Prof. Liu Feng from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS) has made a groundbreaking discovery. The scientists discovered that 250-million-year-old pollen in rocks contained compounds similar to sunscreen, but produced by plants to protect themselves from harmful ultraviolet (UV-B) radiation. 

The research, which was published in Science Advances on January 6, shows that the presence of these compounds suggests that a surge of UV-B played a crucial role in the end-Permian mass extinction event. This event, which took place 250 million years ago, is considered the most severe of the big five mass extinction events and resulted in the loss of nearly 80% of marine and terrestrial species. 

The cause of the mass extinction was a paleoclimate emergency triggered by large-scale volcanic activity in modern-day Siberia. This volcanic activity led to the release of massive amounts of carbon into the atmosphere, causing greenhouse warming and the collapse of the Earth's ozone layer. 

According to Professor Barry Lomax from the University of Nottingham, plants need sunlight for photosynthesis but must protect themselves and especially their pollen from the harmful effects of UV-B radiation. To do this, plants load the outer walls of their pollen grains with compounds similar to sunscreen to ensure successful reproduction. 

The researchers used a method to detect these phenolic compounds in fossil pollen grains from southern Tibet and found higher concentrations in the grains produced during the end-Permian mass extinction and peak phase of volcanic activity. The scientists also found an increase in UV-B-absorbing compounds (UACs) that coincided with a spike in mercury concentration and a decrease in carbon isotopes in the latest Permian deposits. This suggests a close relationship between large-scale volcanic eruptions, global carbon- and mercury-cycle perturbations, and ozone-layer disruption. 

Elevated UV-B levels had far-reaching and long-lasting impacts on the Earth system. Recent studies have shown that elevated UV-B stress reduced plant biomass and terrestrial carbon storage, thereby exacerbating global warming. In addition, higher concentrations of phenolic compounds made plant tissue less digestible, making the environment even more challenging for herbivores. 

According to Dr. Wes Fraser from Oxford Brookes University, volcanic activity on such a catastrophic scale influences all aspects of the Earth system, from direct chemical changes in the atmosphere to reducing the amount of nutritious food available for animals. 

For further information on this research, see "Dying in the Sun: Direct Evidence for Elevated UV-B Radiation at the End-Permian Mass Extinction."