Chicxulub Asteroid Caused End-Cretaceous Mass Extinction, New Study Confirms
The end-Cretaceous mass extinction 66 million years ago eradicated roughly 75% of the animal and plant species on Earth, including whole groups like non-avian dinosaurs and ammonites. Debate lingers over what caused this extinction, with intense volcanic activity in India’s Deccan Traps and the asteroid strike near the site of the small town of Chicxulub in Mexico the most widely supported hypotheses. Now, a team of researchers from the UK has shown that only the Chicxulub impact could have created conditions that were unfavorable for non-avian dinosaurs across the globe. The scientists also show that the massive Deccan volcanism could also have helped life recover from the asteroid strike in the long term.
“We show that the asteroid caused an impact winter for decades, and that these environmental effects decimated suitable environments for dinosaurs,” said Dr. Alfio Alessandro Chiarenza, a researcher in the Department of Earth Science and Engineering at Imperial College London and the Department of Earth Sciences at University College London.
“In contrast, the effects of the intense volcanic eruptions were not strong enough to substantially disrupt global ecosystems.”
“Our study confirms, for the first time quantitatively, that the only plausible explanation for the extinction is the impact winter that eradicated dinosaur habitats worldwide.”
The Chicxulub strike would have released particles and gases high into the atmosphere, blocking out the Sun for years and causing permanent winters.
Volcanic eruptions also produce particles and gases with Sun-blocking effects, and around the time of the mass extinction there were tens of thousands of years of eruptions in the Deccan Traps province.
To determine which factor, the asteroid or the volcanism, had more climate-changing power, the scientists combined traditionally used geological markers of climate and powerful mathematical models with information about what kinds of environmental factors, such as rainfall and temperature, each species of dinosaur needed to thrive.
They were then able to map where these conditions would still exist in a world after either an asteroid strike or massive volcanism.
They found that only the asteroid strike wiped out all potential dinosaur habitats, while volcanism left some viable regions around the equator.
“Instead of only using the geologic record to model the effect on climate that the asteroid or volcanism might have caused worldwide, we pushed this approach a step forward, adding an ecological dimension to the study to reveal how these climatic fluctuations severely affected ecosystems,” said Dr. Alex Farnsworth, a researcher in the School of Geographical Sciences at the University of Bristol.
“In this study we add a modeling approach to key geological and climate data that shows the devastating effect of the asteroid impact on global habitats. Essentially, it produces a blue screen of death for dinosaurs,” said Dr. Philip Mannion, a scientist in the Department of Earth Sciences at University College London.
Although volcanoes release Sun-blocking gases and particles, they also release carbon dioxide, a greenhouse gas.
In the short term after an eruption, the Sun-blockers have a larger effect, causing a ‘volcanic winter.’
However, in the longer term these particles and gases drop out of the atmosphere, while carbon dioxide stays around and builds up, warming the planet.
After the initial drastic global winter caused by the asteroid, the team’s model suggests that in the longer term, volcanic warming could have helped restore many habitats, helping new life that evolved after the disaster to thrive.
“We provide new evidence to suggest that the volcanic eruptions happening around the same time might have reduced the effects on the environment caused by the impact, particularly in quickening the rise of temperatures after the impact winter,” Dr. Chiarenza said.
“This volcanic-induced warming helped boost the survival and recovery of the animals and plants that made through the extinction, with many groups expanding in its immediate aftermath, including birds and mammals.”
The research was published in the Proceedings of the National Academy of Sciences.
Alfio Alessandro Chiarenza et al. Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction. PNAS, published online June 29, 2020; doi: 10.1073/pnas.2006087117