Deadly Dust: What Really Killed the Dinosaurs After the Asteroid Impact

The Chicxulub impact, believed to have caused the mass extinction 66 million years ago, may have resulted in a 15°C global cooling, primarily due to micrometric silicate dust, according to a new study from the Royal Observatory of Belgium. This dust could have disrupted photosynthesis for almost two years, contributing to the extinction event.

Fine dust from pulverized rock generated by the Chicxulub impact likely played a dominant role in global climate cooling and the disruption of photosynthesis following the event. This is suggested by a new study published in Nature Geoscience, in which researchers Cem Berk Cenel, Özgür Karatekin, and Orkun Temel of the Royal Observatory of Belgium contributed.

The Chicxulub meteorite impact has long been thought to have triggered a global impact winter, which led to the demise of the dinosaurs and around 75% of species on Earth at the Cretaceous-Palaeogene (K-Pg) boundary 66 million years ago. However, what effect the various types of debris ejected from the crater had on the climate is debated, and exactly what caused the mass extinction remains unclear.

Previous research has suggested that sulfur released during the impact and soot from post-impact wildfires constituted the main drivers of an impact winter, and not the ejection of silicate dust into the atmosphere. However, this hypothesis was based so far on a limited knowledge of the actual size properties of the dust particles.

Paleoart reconstruction depicting North Dakota in the first months following the Chicxulub impact event 66 million years ago, showing a dark, dusty, and cold world in which the last non-avian dinosaurs, illustrated with a Dakotaraptor steini, were on the edge of extinction. Credit: Mark A. Garlick

New Insights from the Royal Observatory of Belgium

To evaluate the roles of sulfur, soot, and silicate dust on the post-impact climate, Cem Berk Senel, Orkun Temel, and Özgür Karatekin, scientists from the Royal Observatory of Belgium (ROB), developed a new paleoclimate model, specialized to simulate the climate and biotic response following the Chicxulub impact. These simulations were carried out by incorporating new, high-resolution geological field data from a location in North Dakota, USA.

Sediment samples were collected and measured using laser-diffraction grain-size analysis by Pim Kaskes and colleagues at Archaeology, Environmental Changes & Geo-chemistry (AMGC) at the Vrije Universiteit Brussel (VUB) and the Vrije Universiteit Amsterdam (VUA).

“We specifically sampled the uppermost millimeter-thin interval of the Cretaceous-Paleogene boundary layer. This interval revealed a very fine and uniform grain-size distribution, which we interpret to represent the final atmospheric fall-out of ultrafine dust related to the Chicxulub impact event. The new results show much finer grain-size values than previously used in climate models and this aspect had important consequences for our climate reconstructions,” explains Kaskes.

Conceptual model of the Chicxulub impact plume showing different stages of (a) production, and (b) transport and deposition of the impact-generated ejecta (not to scale). (c) Paleoclimate model simulations showcasing the time evolution of the dust-induced photosynthetic active radiation flux across the planet following the Chicxulub impact 66 million years ago. Credit: Modified from Senel et al., 2023; Nature Geoscience

The Role of Silicate Debris

The researchers discovered that the size distribution of silicate debris (approximately 0.8–8.0 µm) revealed a larger role for fine dust than previously appreciated.

Cem Berk Senel (ROB), the lead author, describes: “The new paleoclimate simulations show that such a plume of micrometric silicate dust could have remained in the atmosphere for up to 15 years after the event, contributing to global cooling of the Earth’s surface by as much as 15 °C in the initial aftermath of the impact.”

This timescale, according to co-authors Steven Goderis and Philippe Claeys (both VUB-AMGC), is consistent with the recent global iridium layer observations from the Chicxulub impact structure, where the final atmospheric settling of fine-grained impactor material in the dust cloud was estimated to be less than 20 years.

Paleoclimate model simulations show the rapid dust transport across the planet, indicating thatthe Paleogene world was encircled by the silicate dust ejecta within a few days following the Chicxulub impact event. Credit: Simulations by Cem Berk Senel

Furthermore, the authors find that dust-induced changes in solar irradiance may have shut down photosynthesis for almost two years post-impact. The prolonged disruption in photosynthesis constitutes a sufficiently long timescale to pose severe challenges for both terrestrial and marine habitats. Biotic groups that were not adapted to survive the dark, cold, and food-deprived conditions for almost two years would have experienced mass extinctions.

This matches the paleontological records, according to co-author Johan Vellekoop (KU Leuven and Royal Belgian Institute of Natural Sciences), which show that fauna and flora that could enter a dormant phase (for example, through seeds, cysts, or hibernation in burrows) and were able to adapt to an omnivorous diet, not dependent on one particular food source (for example, deposit feeders), generally better survived the K-Pg event.

The authors suggest that the silicate dust, along with soot and sulfur, played a major role in blocking photosynthesis and sustaining an impact winter long enough to cause the catastrophic collapse of primary productivity, triggering a chain reaction of extinctions.

Overview of the Cretaceous-Paleogene boundary in North Dakota (USA). The sediments indicate a river and swamp-like environment at the end of the age of the dinosaurs. The pink-brown layer yields ejecta debris derived from the Chicxulub impact event and the grain-size data from this interval were used as input parameters for the paleoclimate modeling study. Credit: Pim Kaskes

Implications and Planetary Defense

“The Chicxulub-sized impacts by kilometer-sized asteroids causing mass extinction events are rare, however, small- and medium-sized asteroids in the range of 100 meters are far more common in the Solar System and can cause destruction on a regional to national scale,” says Özgür Karatekin (ROB).

The European Space Agency’s Hera asteroid mission for planetary defense is Europe’s contribution to an international planetary defense experiment to which authors of the present research from the Royal Observatory of Belgium and VUB are contributing. The Hera mission will validate the kinetic impactor asteroid deflection technique and provide scientific information, thereby increasing our understanding of asteroid geophysics and impact processes.

The HELOS laser-diffraction grain-size analyzer at the Sedimentology Lab of the Vrije Universiteit Amsterdam. This instrument was used to measure the size properties of the Cretaceous-Paleogene boundary sediments depicted in the foreground. Credit: Pim Kaskes

Reference: “Chicxulub impact winter sustained by fine silicate dust” by Cem Berk Senel, Pim Kaskes, Orkun Temel, Johan Vellekoop, Steven Goderis, Robert DePalma, Maarten A. Prins, Philippe Claeys and Özgür Karatekin, 30 October 2023, Nature Geoscience.
DOI: 10.1038/s41561-023-01290-4

This research has been supported by Belgian Federal Science Policy (BELSPO) through the Chicxulub BRAIN-be (Belgian Research Action through Interdisciplinary Networks) project, which is a collaboration between the Royal Observatory of Belgium, Vrije Universiteit Brussel, and the Royal Belgian Institute of Natural Sciences. The authors also acknowledge the support of Research Foundation-Flanders (FWO) grants as well as a FED-tWIN project.

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