That the 200-kilometer (125-mile) Chicxulub crater in present-day Mexico formed when the asteroid struck, ultimately killing three quarters of life on the planet, is a fact that most scientists agree. But the trajectory and direction of this impact is still a matter of debate.
In a new study, an international team of researchers said their 3D simulations showed that the asteroid hit at an angle of 40 to 60 degrees – what Gareth Collins, a professor of planetary science at the science department of land and engineering of Imperial College London, described it as a worst case scenario for dinosaurs.
“We know this was one of the worst-case scenarios for impact mortality, because it put more dangerous debris in the upper atmosphere and scattered it everywhere – which led to a nuclear winter,” he added.
Such a strike has likely sparked billions of tons of sulfur and other gases into the atmosphere, blocking the sun and leading to a dramatic cooling of the Earth’s climate.
“This was based on a different interpretation of geophysical data, which our work overturns, and observations at the time that suggested that the ejecta from the crater was asymmetric, with more ejecta in North America (northwest) than elsewhere”, he explained via email, referring to the material that was expelled as a result of the impact.
“More recent observations have shown that the ejecta distribution is more or less symmetric.”
The team of researchers from Imperial College London, the University of Freiburg in Germany and the University of Texas in Austin examined the shape and structure of the crater and the rocks extracted by drilling the crater, which contained evidence of the extreme forces generated from the impact.
“Despite being buried under nearly a kilometer of sedimentary rocks, it is remarkable that geophysical data reveal so much about the structure of the crater – enough to describe the direction and angle of the impact,” said Auriol Rae, postdoctoral researcher at the University of Friborg and co-author of the study.
This information and other data were used to build a model that simulated the formation of the Chicxulub crater, determining the direction from which the asteroid came and the angle. The team considered four different angles: 90, 60, 45 and 30 degrees.
The authors said they considered 60 degrees to be the most likely angle due to the relationship between three points of the crater – its center, a mountain ring made of heavily fractured rock within the crater rim and the center of rocks of the dense and elevated mantle some 30 kilometers under the crater.
On the Chicxulub crater, these characteristics are aligned in the south-west-north-east direction, according to the study, and the team’s 3D simulations at a 60-degree angle reproduced these observations almost exactly.
The authors said that that angle of impact would have produced more climate-modifying gases such as sulfur and carbon dioxide than a very superficial or almost vertical impact.
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