Approximately 66 million years ago a roughly 17-kilometer (10.6 miles) wide asteroid struck Earth, flinging billions of tons of sulfur up into the atmosphere, and spelling a cool end for 75 percent of life on the planet – including non-avian dinosaurs. But new simulations of the colossal impact suggests that these dinos had really really bad luck, as at either a shallower or steeper angle of descent, the asteroid may not have completely crashed the dinosaurs' party.
“For the dinosaurs, the worst-case scenario is exactly what happened,” Dr Gareth Collins, of Imperial College London, UK, and lead author of the research published in Nature Communications, said in a statement. “The asteroid strike unleashed an incredible amount of climate-changing gases into the atmosphere, triggering a chain of events that led to the extinction of the dinosaurs. This was likely worsened by the fact that it struck at one of the deadliest possible angles.”
The international team of researchers found that the site of the asteroid impact, the 200-kilometer (124-mile) wide Chicxulub crater in Mexico, was likely formed by a space rock on a steep trajectory, between 45 and 60 degrees to the horizontal, approaching from the north-east. This caused a near symmetrical distribution of material to be ejected from the porous carbonate and evaporite rocks and unleashed more climate-changing gases per impactor mass than any other scenario tested. It was this release of vast amounts of carbon dioxide, sulfur, and water vapor that would have blocked the Sun’s rays – preventing photosynthesis in plants, rapidly cooling the climate, and ultimately contributing to the mass extinction event.
“Our simulations provide compelling evidence that the asteroid struck at a steep angle, perhaps 60 degrees above the horizon, and approached its target from the north-east,” Collins continued. “We know that this was among the worst-case scenarios for the lethality on impact, because it put more hazardous debris into the upper atmosphere and scattered it everywhere – the very thing that led to a nuclear winter.”
In combination with these 3D simulations, which were the first to fully model the event from start (the impact) to finish (the final crater formation), the team used geophysical data from the site in Mexico. Drill samples from recent studies showed evidence of the extreme impact forces and the shape and subsurface of the crater informed the possible impact angle and direction.
“Despite being buried beneath nearly a kilometer of sedimentary rocks, it is remarkable that geophysical data reveals so much about the crater structure – enough to describe the direction and angle of the impact,” co-author Dr Auriol Rae of the University of Freiburg, Germany said in a statement.
In fact, the alignment of the crater center, the center of the peak ring (a ring of mountains made of heavily fractured rock inside the crater rim), and the center of the 30-kilometer (18.6-mile) deep uplifted mantle rocks, was a pivotal piece of evidence that supported the simulation results from a 60-degree asteroid trajectory.
Mapping the continual movement of the crater has not only aided in the team’s understanding of this dinosaur-dooming impact, but could potentially help others in their study of large craters, even on other planets.
“Large craters like Chicxulub are formed in a matter of minutes, and involve a spectacular rebound of rock beneath the crater,” co-author Dr Thomas Davison, also of Imperial College London, explained. “Our findings could help advance our understanding of how this rebound can be used to diagnose details of the impacting asteroid.”