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A Mount Everest-sized rock smashed into our planet 66 million years ago, sending up clouds that blotted out the sun and killed most creatures on Earth.
But it could have been very different, scientists say – as the rock hit Earth at the “deadliest possible angle”.
The burning cloud that erupted from the crater incinerated everything within hundreds of miles and triggered a “nuclear winter” that wiped out the dinosaurs.
But if the doomsday asteroid’s approach had been shallower or steeper, there would have been another outcome, according to the first 3D computer simulation of the impact.
Lead author Dr Gareth Collins, of Imperial College London, said: “For the dinosaurs, the worst-case scenario is exactly what happened.”
The impact left a 1200-mile-wide crater, vaporising rock and sending billions of tons of sulphur and carbon dioxide into the prehistoric skies.
Temperatures plunged, acid rain fell and 75 percent of life was wiped out, including the dinosaurs.
Collins said: “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 it struck at one of the deadliest possible angles. Our simulations provide compelling evidence the asteroid struck at a steep angle – perhaps 60 degrees above the horizon – and approached its target from the north-east.
“We know 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.”
Collins and his colleagues used a model that considered four different angles – 90, 60, 45 and 30 degrees.
They used geophysical data from the site to reproduce the whole event, from the initial impact to the moment the crater, called Chicxulub, was created 66 million years ago.
This included recent results from an offshore drilling expedition that brought up rocks containing evidence of the extreme forces that were generated.
Pivotal to diagnosing the angle and direction of impact was the relationship between the centres of the crater and the “peak ring” – a circle of heavily-fractured mountains inside the rim – and mantle rocks 20 miles underground.
An angle of 60 degrees reproduced these observations almost exactly, the researchers said.
Co-author Dr Auriol Rae, of the University of Freiburg in Germany, said: “Despite being buried beneath nearly a kilometre (0.62 mile) of sedimentary rocks, it is remarkable geophysical data reveals so much about the crater structure – enough to describe the direction and angle of the impact.”