Earlier research suggested that the mass extinction event that eliminated the dinosaurs was driven by a significant release of sulfur from rocks in the Chicxulub impact crater 66 million years ago. However, a new investigation led by Katerina Rodiouchkina from Luleå University of Technology in Sweden and universities in Belgium challenges this perspective. By utilizing innovative measurements of sulfur in the Cretaceous-Paleogene (K-Pg) boundary layer, they have shown that the importance of sulfur in the extinction process might have been overestimated.
About 66 million years ago, an asteroid approximately 10-15 kilometers wide collided with the Yucatán Peninsula (present-day Mexico), creating a massive 200-kilometer-wide crater. This collision instigated a series of catastrophic events, including drastic climate changes, which ultimately led to the extinction of non-avian dinosaurs and around 75% of Earth’s species. A key factor in this devastation is likely the “impact winter,” which occurred due to the substantial release of dust, soot, and sulfur into the atmosphere. This caused severe cold and darkness, disrupting global photosynthesis and impacting ecosystems for years to decades after the event.
Many previous studies regarded sulfur as the primary factor influencing the cooling and extinction that followed the impact. Nonetheless, estimates of sulfate aerosols released due to the vaporization of rocks in Mexico have varied significantly across different studies, sometimes varying by a factor of more than one hundred. These discrepancies arise from uncertain variables, such as the quantity of sulfur-containing rocks at the impact site, along with factors like the asteroid’s size, speed, angle of impact, and subsequent pressures affecting sulfur-rich minerals.
In this recent study, Rodiouchkina and her team analyzed sulfur concentration and isotopic composition from new drill cores of impact rocks in the crater area, alongside detailed chemical analyses from K-Pg boundary sediments worldwide. This allowed them to provide the first empirical estimate of the volume of sulfur released into the atmosphere following the Chicxulub impact.
“Rather than concentrating only on the impact itself, we focused on what happened afterward,” says chemist Katerina Rodiouchkina. “We began by examining the sulfur signature of the rocks in the crater region that contributed to the sulfate aerosols in the atmosphere. These aerosols spread globally and were later deposited back onto the Earth’s surface over months and years. We detected sulfur across K-Pg boundary layers in sediments worldwide and analyzed the isotopic changes to differentiate impact-related sulfur from natural sources, allowing us to calculate the total sulfur released through mass balance.”
The researchers found that approximately 67 ± 39 billion tons of sulfur were emitted, which is about five times less than earlier numerical model estimates suggested. This indicates a less severe “impact winter,” leading to a milder temperature drop and quicker climate recovery, which might have allowed at least 25% of species on Earth to survive post-impact. Although sulfur remains a major contributor to global cooling, a recent study from the Royal Observatory of Belgium and VUB points to a significant release of fine dust as a key factor in causing a two-year dark period, which hindered photosynthesis and exacerbated environmental damages.
This research was a collaboration involving Luleå University of Technology, Ghent University (UGent), Vrije Universiteit Brussel (VUB), the Royal Observatory of Belgium (ROB), Université Libre de Bruxelles (ULB), Leibniz Institute for Baltic Sea Research Warnemünde (IOW), University of Greifswald, University of Rostock, Australian Laboratory Services (ALS) Scandinavia AB, Katholieke Universiteit Leuven (KU Leuven), and the Royal Belgian Institute of Natural Sciences (RBINS). The study received support from the Research Foundation Flanders (FWO) through the EOS-Excellence of Science initiative (project ET-HoME) and Hercules funding for the acquisition of a multi-collector ICP-mass spectrometer at UGent, VUB’s Strategic Research Program, Chicxulub BRAIN-be (Belgian Research Action through Interdisciplinary Networks), and the FED-tWIN project MicroPAST, all facilitated by the Belgian Science Policy Office (BELSPO).
