A New Timeline of the Day the Dinosaurs Began to Die Out

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The giant asteroid’s impact into shallow waters in the Gulf of Mexico 66 million years ago was bad enough. But then an amalgam of additional disasters ensued: Rocks fell from the sky, wildfires ignited and tsunamis inundated distant shorelines.

It was the beginning of the end of the Mesozoic Era when dinosaurs ruled the world.

Scientists released a new record of this day of chaos in Proceedings of the National Academy of Sciences on Monday. Their timeline of the first day of the Cenozoic Era was developed using high-resolution photography, microscopy, computed tomography imaging and magnetic measurements of hundreds of feet of sedimentary rock recently recovered from Chicxulub, one of the largest impact craters on Earth.

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In 2016, researchers drilled deep in waters off the Yucatán Peninsula for the first time into Chicxulub’s peak ring, a circle of mountains within the crater.

This new study, led by Sean P. S. Gulick, a marine geophysicist at the University of Texas at Austin, focuses on a subset of these cores, which are effectively a 430-foot-long sedimentary rock record of the first day after the asteroid impact.

“We normally get to read rock records that give us centimeters per thousand years,” Dr. Gulick said. “We have 130 meters for a day.”

The researchers found that the first day of the Cenozoic was peppered with cataclysms.

When the asteroid struck, it temporarily carved a hole 60 miles across and 20 miles deep. The impact triggered a tsunami moving away from the crater. It also catapulted rock into the upper atmosphere and beyond.

“Almost certainly some of the material would have reached the Moon,” Dr. Gulick said.

The largest pieces of debris rained back down to Earth within minutes, Dr. Gulick and his team say, pelting the scarred landscape with solidifying rock. Smaller particles lingered for longer periods, and glassy blobs known as tektites, formed when falling, molten rock cools, have been found across North America and dated to the Chicxulub impact.

Within about 30 minutes, ocean water began to flood back into the crater through a gap in its northeastern rim, the researchers suggest.

The roughly 300 feet of rock in the peak ring is sorted by size and is evidence of this flooding. “If you throw a bunch of material into water and let it settle, the bigger things fall first and the smaller things take longer to fall,” Dr. Gulick said.

But this flooding was just ripples in a bathtub compared with what was coming next — the water that had been violently displaced by the asteroid’s impact was returning, the scientists say.

Enormous tsunamis, with waves topping several hundred feet, rushed over the crater a few hours after the impact. Created when the asteroid struck the Gulf of Mexico, they reflected off nearby coastlines before barreling back toward the crater. They left behind a four-inch layer of sand and fine gravel in the peak ring containing perylene, a biomarker of soil.

In addition to the raining rocks and tsunamis, the landscape was also ravaged by widespread fires, Dr. Gulick and his team suggest. Fragments of charcoal in the peak ring above the tsunami layer are a sign of impact-induced wildfires, the researchers say. Wildfires could have been triggered by a blast of thermal energy from the impact plume, or by friction-heated rocks raining back down through the atmosphere.

“Probably not everything burned, but certainly there were global wildfires,” Dr. Gulick said.

These results provide “unprecedented insights” into what transpired the first day of the Cenozoic, said Paul Byrne, a planetary geologist at North Carolina State University who was not involved in the research. It’s one thing to suspect impact-triggered chaos based on computer simulations, he said, but “it’s quite another to see it.”

Earlier this year, another research team working in North Dakota reported finding the remnants of an ancient lake containing fossilized fish with tektites in their gills. These animals, they suggested, were likely killed within an hour of the asteroid strike by impact-triggered waves that tossed them onto land. Finding more evidence of the immediate aftermath of the Chicxulub impact will yield important scientific knowledge about the day the dinosaurs began to die out.

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