66 million years ago, a massive asteroid struck Earth, causing a planetary-scale catastrophe. As ecosystems were already suffering from climate disruption caused by the intense volcanic activity that had been shaking the Deccan Traps for several million years, this event was the final blow to the dinosaurs, which then rapidly went extinct.
An Impact Winter Linked to Sulfur or Dust?
While both volcanism and the asteroid played a role, determining the extent of each and the mechanisms at work is still complex. While the influence of massive volcanism is better constrained and appears to have been the dominant factor in this biological crisis, the effects of the impact on the final extinction of the dinosaurs are still poorly understood. The most prevalent hypothesis currently is that the impact led to a drop in global temperatures over several years. While sulfur ejected into the atmosphere at the time of the catastrophe is often blamed for explaining this impact winter, a new study published in Nature Geoscience revisits an old theory.
A 15°C Drop in Global Temperatures for 15 Years
According to the researchers, the impact winter was more likely caused by the enormous quantity of silicate rock dust pulverized by the asteroid’s impact and projected into the atmosphere. The world would have been plunged into darkness, resulting in a decrease of over 15°C in global temperatures for 15 years.
Dust particles have indeed been found at the fossil site of Tanis, which is located 3,000 kilometers from the Chicxulub crater. The size of these particles, ranging from 0.8 to 8 micrometers, correlates with an atmospheric residence time of about 15 years. Scientists suggest that among all the material projected into the atmosphere, 75% would have been dust particles and only 24% sulfur. The remaining 1% would have been fire-related ashes.
These environmental conditions would have prevented photosynthetic processes from functioning and led to the collapse of ecosystems.