Fossil pollen points to radiation pulse during mass extinction
Research on fossilised pollen has given further weight to the theory that a massive pulse of ultraviolet radiation had a major impact on mass extinction event
New research has uncovered that pollen preserved in 250-million-year-old rocks contain compounds that function like sunscreen, these are produced by plants to protect them from harmful ultraviolet (UV-B) radiation.
The findings suggest that a pulse of UV-B played an important part in the end-Permian mass extinction event.
Scientists from China, Germany and the UK, led by Professor Liu Feng from Nanjing Institute of Geology and Palaeontology, have developed a new method to detect plants’ sunscreen-like compounds in fossil pollen grains.
The end-Permian mass extinction event (250 million years ago) is the most severe of the big five mass extinction events with the loss of ~80% of marine and terrestrial species.
This catastrophic loss of biodiversity was a response to a palaeoclimate emergency triggered by the emplacement of a continental-scale volcanic eruption that covers much of modern-day Siberia.
The volcanic activity drove the release of massive amounts of carbon that had been locked up in Earth’s interior into the atmosphere, generating large-scale greenhouse warming. Accompanying this global warming event was a collapse in the Earth’s ozone layer.
Support for this theory comes from the abundant occurrence of malformed spores and pollen grains that testify to an influx of mutagenic UV irradiation.
See also: Tree root evolution ‘triggered’ mass extinction events
fossil pollen grains
Professor Barry Lomax, from the University of Nottingham, UK, explained: “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.”
Feng added: “We have developed a method to detect these phenolic compounds in fossil pollen grains recovered from Tibet, and detected much higher concentrations in those grains that were produced during the mass extinction and peak phase of volcanic activity.”
Elevated UV-B levels can have even further-reaching and longer-lasting impacts on the entire Earth system. Recent modelling studies have demonstrated that elevated UV-B stress reduces plant biomass and terrestrial carbon storage, which would exacerbate global warming.
The increased concentration of phenolic compounds also makes plant tissue less easily digestible, making a hostile environment even more challenging for herbivores.
Summarising the groups findings, Dr Wes Fraser based at Oxford Brookes University, UK, commented: “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.”
The research is published in Science Advances.
Image: Alisporites tenuicorpus the pollen grain used in this work. Note a human hair is approximately 70mm so the samples analysed are about half the width of a human hair. © Liu Feng/ Nanjing Institute of Geology and Palaeontology.