Depletion of the ozone layer led to mass extinction

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Palaeobotanists analyse plant fossils 252 million years old

Prof. Benjamin Bomfleur (right) and Dr. Phillip Jardine discuss their samples in
Prof. Benjamin Bomfleur (right) and Dr. Phillip Jardine discuss their samples in the lab. © Münster University - Peter Leßmann
252 million years ago, there occurred the greatest mass extinction in the history of the Earth up to that time: three-quarters of life on land and up to 95 percent of marine species vanished within just a few thousand years. This far-reaching event at the end of the Permian period marked the transition to a new age - that of the dinosaurs. The catastrophic extent of this mass extinction in the oceans has been known and well documented for a long time now. "However, there has been far less research undertaken into the extent to which life on land was affected by this event," says Prof. Benjamin Bomfleur.

Bomfleur’s team of researchers at the Institute of Geology and Palaeontology at Münster University have now taken a decisive step forward: they determined that the extinction occurred at the same time as huge volcanic eruptions in what is today Siberia. These eruptions were so massive that they caused long-term changes to the composition of the Earth’s atmosphere and, as a result, to the development of the global climate. "Our studies provide clear evidence of a concrete mechanism - the depletion of the ozone layer - which may explain the worldwide crisis in biodiversity happening on land at that time," says Dr. Phillip Jardine.

In order to understand how these things interrelated, the Münster team and international colleagues studied the Qubu profile, a region in southern Tibet about 30 kilometres north of Mount Everest. Here are to be found rock sequences in high-resolution quality which cover this geological period. "Fossils of both marine and terrestrial organisms are well preserved there, layer by layer," says Benjamin Bomfleur. "Up to now, it was predominantly animal fossils which were examined, while the plant fossils - and in particular the pollen and spores occurring en masse in sedimentary rocks - were not researched sufficiently at all."

From a sequence of rock samples encompassing the period in which the extinction occurred, the researchers selected pollen grains from one group of plants. Using infrared spectrometry, they were able to determine the composition of the exospores. "The analysis showed a sudden rise in components absorbing UV-B - a rise which coincides exactly with the highpoint of the volcanic activity. We might also say that the plants developed their own protection against the sun because of the ozone layer having been destroyed. As a result, they achieved a resilience to ultraviolet radiation in their pollen grains which were susceptible to the sun’s radiation," says Phillip Jardine, explaining the results.

In today’s context, what particularly springs to mind is a comparison with the threat of an ozone catastrophe in the last century. Scientific findings on the damaging effects of halocarbons on the ozone layer led to the signing of the Montreal Protocol in 1987, which prohibited these halocarbons and ensured the regeneration of the ozone layer. "If the necessary steps hadn’t been taken at that time to avoid further depletion of the ozone," concludes Benjamin Bomfleur, "the Earth would probably have been affected once again by a catastrophic collapse of the protective ozone layer - comparable, perhaps, to that which occurred 252 million years ago which we were able to demonstrate in our work." The results of the study were published recently in the journal Science Advances.

Kathrin Kottke

This article is from the university newspaper wissen