The asteroid was so large that, even at the moment of impact, the top of it might have still towered more than a mile above the cruising altitude of a 747. “In its nearly instantaneous descent, it compressed the air below it so violently that it briefly became several times hotter than the surface of the sun,” is how mass-extinction authority, Peter Brannen describes the Chicxulub asteroid impact 66 million years ago which struck the Earth off the coast of Mexico at the end of the Cretaceous, creating an epic impact winter and a momentous, transitional day for the history of life on Earth.
“The pressure of the atmosphere in front of the asteroid started excavating the crater before it even got there,” geophysicist Mario Rebolledo at the Centro de Investigación Científica de Yucatán, told Brannen. “Then, when the meteorite touched ground zero, it was totally intact. It was so massive that the atmosphere didn’t even make a scratch on it. it would have been a pleasant day one second and the world was already over by the next. As the asteroid collided with the earth, in the sky above it where there should have been air, the rock had punched a hole of outer space vacuum in the atmosphere. As the heavens rushed in to close this hole, enormous volumes of earth were expelled into orbit and beyond—all within a second or two of impact.”
In a new study, a research team from Imperial College London, the University of Bristol and University College London has shown that the asteroid impact created conditions responsible for the demise of dinosaurs across the globe, challenging the claims by researchers who have suggested that tens of thousands of years of large volcanic eruptions may have been the actual cause of the extinction event, which also killed off almost 75% of life on the planet.
The researchers also show that the massive volcanism could also have helped life recover from the asteroid strike in the long term. Their results are published today in Proceedings of the National Academy of Sciences.
Lead researcher Dr Alessandro Chiarenza, who conducted this work whilst studying for his PhD in the Department of Earth Science and Engineering at Imperial, said: “We show that the asteroid caused an impact winter for decades, and that these environmental effects decimated suitable environments for dinosaurs. 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 asteroid 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 at the Deccan Traps, in present-day India.
To determine which factor, the asteroid or the volcanism, had more climate-changing power, researchers have traditionally used geological markers of climate and powerful mathematical models. In the new paper, the team combined these methods 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 co-lead author of the study Dr Alex Farnsworth, from the University of Bristol.
“In this study we add a modelling 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,” commented co-lead author of the study Dr Alex Farnsworth, from the University of Bristol.
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,” said Chiarenza. “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 Daily Galaxy, Andy Johnson, via Imperial College of London
Image at the top of the page: Illustration by Fabio Manucci of an individual of Ankylosaurus magniventris, a large armoured dinosaur species, witnesses the impact of an asteroid, falling on the Yucatán peninsula 66 million years ago. Not even its large size and thick armour sheltered its kind from the violence of this cosmic disaster.