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Geological inquiry by earth scientist Remco Bos has found that the quarry near the Dutch town of Winterswijk offers a glimpse into a massive extinction event from the geologic past. For the first time, evidence has been uncovered for the end-Triassic mass-extinction in the subsurface of the Netherlands. This was not the mass-extinction event that brought an end to the age of dinosaurs, but rather cleared the path for their further evolution and subsequent dominance over the Earth. The sediments marking this dramatic event are literally lying beneath your feet around Winterswijk.

Around two hundred million years ago, one fourth of all animal species in the oceans went extinct, along with countless reptile species on land. This extinction event marked the end of the Triassic Period and ushered in the Jurassic Period, setting the stage for the dominance of dinosaurs. Scientists have long suspected that widespread and large-scale volcanism was responsible for this event. Earlier this year, Bos published a scientific article showing that volcanic eruptions are linked to global mercury poisoning which played a crucial role in the extinctions of land plants. This highly toxic metal remained in soils for another two million years and affected the recovery following the extinction. He derived this interpretation from the large numbers of deformations in fossilized fern spores in ancient sediments from Germany.

Deforestation

Bos has now discovered that the end-Triassic extinction event has also left its traces in the Netherlands. He and his colleagues from Utrecht ľ¹Ï¸£ÀûÓ°ÊÓ and the Geological Survey of the Netherlands (TNO) recovered and sampled the upper 30 meters of sediments near the quarry in Winterswijk using a sophisticated drilling installation. Laboratory examination of the recovered sediments revealed micro-fossils (pollen and spores) from the last stage of the Triassic. These micro-fossils further indicate a progressive deforestation during this period which likely contributed to the extinction of animals. Previous research had already shown that tree-type vegetation of the latest Triassic gradually disappeared and made way for opportunistic ferns; hardy plants that easily settle in disturbed environments. Additional geochemical analyses of the recovered material showed that the ecological disruptions were caused by abrupt and severe climate change linked to massive volcanic eruptions.

A more complete story

The publication by Remco Bos and colleagues has filled in some of the gaps in the story of the end-Triassic mass-extinction. A comparison of these findings with results from other sedimentary records across Europe confirm the progression and scale of the extinction event. It also emphasises the importance of the Winterswijk quarry for the geology of the Netherlands, because there are very few places where such ancient rock strata can be found near the surface. That is because most of the surface sediments in the Netherlands are much younger and are roughly 10000 years old. Therefore, regions such as those near Winterswijk are treasure troves for geologists studying ancient climate change and the evolution of life.

Waves of extinction

Five major extinction events are known from geologic history. The most well-known is the end-Cretaceous extinction (66 million years ago) when a major asteroid struck the Earth, killing the dinosaurs, although modern birds are evidence that some lineages of dinosaurs did survive this event. The most severe mass-extinction occurred at the end of the Permian Period (251 million years ago), wiping out nearly 95% of all marine animals and was the closest life came to vanishing from this Earth. Both these extinctions events co-occurred with large-scale volcanic eruptions similar to the end-Triassic mass-extinction. Research into mass-extinction events and potential causes can help us identify the risk factors that can lead to biodiversity loss and extinction. The current decline in biodiversity is now considered to be a potential sixth wave of mass-extinction.

Article

Remco Bos, Roel-Jan van Zonneveld, Jelle Reumer, Geert-Jan Vis, Nico Janssen, Teun Everwijn, Appy Sluijs, Bas van de Schootbrugge, ‘A high-resolution palynological and geochemical study on the onset of the end-Triassic mass-extinction based on a new cored succession at Winterswijk (the Netherlands)’, Geological Magazine, Volume 161 (2024), e17,