In the hours after the dinosaur-killing asteroid hit Earth 66 million years ago, the planet was transformed—ravaged by wildfires and a huge tsunami, before being plunged into darkness in an event that would kill off 75 percent of life.
By studying a core sample from the peak ring of the 93-mile-wide Chicxulub crater—ground zero of the impact—a team of scientists has been able to reconstruct the immediate aftermath of the impact. Their paper, titled The first day of the Cenozoic and published in PNAS, shows how the impact of the asteroid deposited about 40 to 50 meters of rock within just a few minutes of hitting the ocean floor.
The land surrounding it was vaporized from the thermal energy and the water in the sea was sent hurtling away in the form of an enormous tsunami. Previous research indicates this wall of water could have reached about a mile in height. Sean Gulick, lead author of the latest paper, said the wave would have been at least hundreds of meters high—and that it was traveling around the speed of a jet plane. Over the next few hours, the ocean water started to make its way back, filling in the crater and depositing a different layer of debris.
Within this layer was charcoal, the researchers discovered. This, they say, is evidence of huge wildfires that would have stretched for hundreds and hundreds of miles. The team also found an absence of sulfur in the deposits—which is unusual as the area is known for having sulfur-rich rocks. This indicates the impact caused a reaction leading to the release of sulfate aerosols—which caused the long period of darkness and global cooling that is believed to have killed off the dinosaurs.
"If you were on Earth and within 1500 kilometers (930 miles) of the impact your view would have been very short as the asteroid comes in at 20 kilometers per second and hence a blink of the eye," Gulick told Newsweek. "Then the energy and thermal effects radiate out from the impact site at various speeds up to the speed of light.
"So effectively within 1500 kilometers you would have seen very little before being incinerated. If you were elsewhere on Earth the first effect might well be the earthquake energy arriving through the ground from the impact or perhaps the arrival of ejecta from the crater raining down and causing heating and wildfires.
"The sky would darken and shortly after the heating from the incoming ejecta the temperatures globally would start to plummet as a sulfate aerosol haze surrounds the planet. The Earth would likely no longer look like the familiar blue marble from space and it would take perhaps as long as two decades to clear again fully."
The team believes the amount of sulfur released into the atmosphere has been underestimated. Current estimates suggest 325 gigatons of sulfur was released—four times more than the eruption of Krakatoa in 1883, which caused global temperatures to plummet by 2.5 degrees Celsius.
"The aerosols would leave the crater at kilometers per second speed and thus blanketing the Earth in hours to days," Gulick said. "Like with sunset, as soon the solar energy is blocked, temperatures fall rapidly."
"We fried them and then we froze them," he said in a statement. "Not all the dinosaurs died that day, but many dinosaurs did."
Commenting on the findings, Jay Melosh, from Purdue University and who was not involved in the study, said this research helps expand our understanding of what happened when the asteroid hit. "It was a momentous day in the history of life, and this is a very clear documentation of what happened at ground zero," he said in a statement.
https://www.newsweek.com/dinosaur-asteroid-impact-tsunamis-wildfire-darkness-1458456
2019-09-10 10:49:09Z
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