Fine particles heralded the end of the dinosaurs

Paleoart reconstruction of North Dakota in the first months after the Chicxulub
Paleoart reconstruction of North Dakota in the first months after the Chicxulub meteorite impact 66 million years ago. It shows a dark, dusty and cold world in which the last non-flying dinosaurs, illustrated here with a Dakotaraptor steini , were on the verge of extinction. Reconstruction by Mark A. Garlick.

Fine dust from pulverized rock released by the Chicxulub meteorite impact 66 million years ago played a dominant role in the cooling of the climate, the disruption of photosynthesis and the mass extinction in which most dinosaurs went extinct.

Until now, the precise circumstances of the mass extinction, such as the effect of the different types of impact material ejected from the crater on global climate were unclear. After previous research, rather than silicate dust emissions into the atmosphere, it was thought that sulfur gas and particles during the impact, and soot from forest fires after the impact, were the main causes of a kind of "nuclear winter. However, this understanding was based on limited knowledge of the physical properties of these dust particles. A new study in Nature Geoscience, involving VUB researchers, shines a new but dark light on the end of the dinosaurs.

Pim Kaskes, Steven Goderis and Philippe Claeys, affiliated with the VUB’s Archaeology, Environmental Changes & Geo-chemistry (AMGC) research group, investigated the grain size of those dust particles with laser-diffraction grain-size analyses at the Vrije Universiteit Amsterdam. Kaskes sampled the dust particles at a geological site in North Dakota in the United States. "We specifically sampled the upper millimeter thin interval of the Cretaceous-Paleogene boundary layer. This interval showed a very fine and uniform grain-size distribution, which we interpret as the out-of-air settling of particulate matter that we can link to the meteorite impact. The new results show much finer grain sizes than previously used in climate models and this aspect has important implications for our climate reconstructions," said Kaskes, who successfully defended his doctoral thesis on the Chicxulub meteorite impact at VUB on April 26 this year.

To investigate the role of sulfur, soot and silicate dust on post-impact climate, Cem Berk Senel, Orkun Temel and Özgür Karatekin, scientists at the Royal Observatory of Belgium (ROB), developed a new paleoclimate model. The new field data allowed them to better simulate the climatic and biological response after the Chicxulub impact. The new model simulations show that a plume of micrometric silicate dust may have remained in the atmosphere for as much as 15 years after the impact. This contributed to global cooling of the Earth’s surface by as much as 15 degrees Celsius. According to Steven Goderis and Philippe Claeys, this time scale matches the insights from a recent discovery of a clay layer, rich in the chemical element iridium, in the middle of the Chicxulub impact crater in Mexico. The iridium is linked to the meteoritic dust that eventually settled back over a period estimated at 20 years.

In addition, the authors found that the particulate matter blocked solar radiation, shutting down photosynthesis on Earth for nearly two years. Plants and animals that were not adapted to survive the dark, cold and nutrient-poor conditions for nearly two years would have died out en masse. This is consistent with data from fossils, according to coauthor Johan Vellekoop (KU Leuven and Royal Belgian Institute of Natural Sciences):

"Flora and fauna that could enter a resting phase (for example, through seeds, cysts or overwintering in burrows) and adapt to a generalist lifestyle, not dependent on one particular food source, would generally survive the meteorite impact better."
"Asteroids larger than one kilometer, which can potentially cause mass extinctions, are rare," says Özgür Karatekin (ROB), "But small and medium-sized asteroids in the range of 100 meters are much more common in the Solar System and can cause devastation on a regional to national scale."

The European Space Agency’s Hera planetary defense mission is Europe’s contribution to an international planetary defense experiment. - The goal of the mission is to provide scientific information on the geophysics of asteroids and impact processes in general. The authors of this research affiliated with the ROB and the VUB, are participating in this.

Reference :

Cem Berk Senel, Pim Kaskes, Orkun Temel, Johan Vellekoop, Steven Goderis, Robert DePalma, Maarten A. Prins, Philippe Claeys, Özgür Karatekin. Chicxulub impact winter sustained by fine silicate dust. Nature Geoscience (2023). DOI: 10.1038/s41561’023 -01290-4

This research was supported by the Federal Science Policy Office (BELSPO) through the Chicxulub BRAIN-be project, a collaboration between the Royal Observatory of Belgium (ROB), the Free University of Brussels (VUB) and the Royal Belgian Institute of Natural Sciences (KBIN). The authors also thank the support of grants from the Fonds Wetenschappelijk Onderzoek - Vlaanderen (FWO) and a FED-tWIN project. The study was published in the scientific journal Nature Geoscience.