The asteroid that killed the dinosaurs struck at a perfect angle to inflict maximum planetwide damage, a study found

Chase StoneAn artist’s depiction of the moment the Chicxulub asteroid struck 66 million years ago.

When a 6-mile-wide asteroid struck the Earth 66 million years ago, it doomed 75% of life on the planet.

The impact, which occurred in present-day Mexico, spurred a mile-high tsunami and wildfires. It instantly acidified the oceans. But the killing stroke for many land-based species was the release of billions of tons of sulphur that blotted out the sun and cooled the planet. The dinosaurs fried, then froze.

According to a study published this week in the journal Nature Communications, if the Chicxulub asteroid had hit Earth at a different angle, some of that devastating fallout may not have happened.

The researchers discovered that the space rock struck at a 60-degree angle, which they said “constitutes the worst-case scenario” in terms of how much carbon dioxide and sulphur was ejected into the atmosphere.

“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,” Gareth Collins, lead author of the study, said in a press release. “This was likely worsened by the fact that it struck at one of the deadliest possible angles.”

An impact that blotted out the sun

Donald Davis/NASAThis painting depicts an asteroid slamming into tropical, shallow seas of the sulphur-rich Yucatan Peninsula in what is today southeast Mexico. The aftermath of this immense asteroid collision, which occurred approximately 65 million years ago, is believed to have caused the extinction of the dinosaurs and many other species on Earth.

To better understand how and from which direction the impact happened, Collins and his colleagues examined rocks from the crater.

When the asteroid hit, it punched a hole in the Earth. Most of the rock in the area was vaporized, but some of the remaining rock in the crater’s centre surged back up, creating a plateau. Had the asteroid hit straight on, that plateau would have been even (picture a rock dropped into mud from above), but instead, it has a 60-degree slope (picture a skid mark from a rock thrown sideways into mud).

The researchers also found that the angles of the rocks at the centre of the plateau and at part of the outer rim of the crater aligned, which indicated the direction the asteroid moved as it created the giant skid mark.

This told the team that the space rock hit from the northeast and careened southwest. They simulated that crash using a 3D computer model, and found that when they inputted a 60-degree impact angle, the results matched geologic data from the present-day crater almost exactly.

The study authors concluded that the asteroid hit the planet at a speed of 12 miles per second (43,200 mph).

Within a minute of the impact, the asteroid had bored a hole nearly 100 miles wide into the seafloor, vaporizing sulphur-rich rocks as it skidded deeper into the Earth. That created a bubbling pit of molten rock and super-hot gas. The contents of that fiery cauldron skyrocketed, creating a mountain-high plume of gaseous sulphur and Co2 that blotted out the sun for decades afterwards.

According to a previous study, at least 357 billion tons (325 billion metric tons) 0f sulphur entered the atmosphere.

‘Lethal on impact’

According to the study authors, impacts that occur at a steep angle, between 30 and 60 degrees, are more efficient at vaporizing rocks.

These steep impacts eject two to three times more C02 and other climate-changing gases into the atmosphere than vertical impacts (when the asteroid falls straight down into the Earth).

Asteroid meteor armageddon shutterstockVadim Sadovski/ShutterstockAn artist’s depiction of an asteroid.

If the Chicxulub asteroid had hit at a shallower angle, say less than 30 degrees, the fallout would have been an order of magnitude less, the researchers found. In that case, only 1 million tons of sun-obscuring gases would have entered the sky, not 1 billion.

Instead, the space rock that killed the dinosaurs struck in just the right way for total devastation.

“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,” Collins said.

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