‘Sunscreen’ in ancient pollen ‘points to mass extinction caused by UV radiation’

Experts analysed pollen from 250 million years ago, around the time when close to 80% of the planet’s species disappeared.

Alisporites tenuicorpus, the pollen grain used in the study (Prof Liu Feng/ Nanjing Institute of Geology and Palaeontology/PA)

Sunscreen-like chemicals found in ancient pollen suggest ultraviolet radiation played a part in one of the biggest mass extinctions that took place 250 million years ago, scientists have said.

A team of experts from the UK, Germany and China analysed ancient pollen grains – about half the width of a human hair – preserved in rocks recovered from Tibet.

Within these pollens they found compounds produced by 250-million-year-old plants to protect themselves from harmful ultraviolet (UV-B) radiation.

The experts said their findings, published in the journal Science Advances, add further evidence to the theory that a “pulse of UV-B played an important part at the end Permian mass extinction event”.

Professor Barry Lomax, from the University of Nottingham, said: “Plants require sunlight for photosynthesis but need to protect themselves and particularly their pollen against the harmful effects of UV-B radiation.

“To do so, plants load the outer walls of pollen grains with compounds that function like sunscreen to protect the vulnerable cells to ensure successful reproduction.”

About 250 million years ago, at the end of the Permian period, something killed more than 80% of the planet’s species, in what is thought to be the most severe of the big five mass extinction events.

The event is believed to have been triggered by a massive volcanic eruption, about the size of modern-day Siberia, which then led to large amounts of carbon being pumped into the atmosphere, creating a greenhouse effect.

The sudden warming process affected the ozone layer, causing it to weaken, and exposing plants and animals to the harmful effects of UV-B radiation.

The scientists said that other discoveries of malformed spores and pollen grains from this time period also add further evidence of the destruction caused by UV irradiation.

Dr Wes Fraser, from Oxford Brookes University, said: “Volcanism on such a cataclysmic scale impacts on all aspects of the Earth system, from direct chemical changes in the atmosphere through changes in carbon sequestration rates, to reducing volume of nutritious food sources available for animals.”