Science & Technology

New Research Shows What Happened the Day the Dinosaur-Killing Asteroid Struck Earth

The asteroid struck Earth with the force of 100 million atomic bombs. The energy released by its impact set fire to trees thousands of miles away and triggered a tsunami that sent seawater rushing hundreds of miles inland. New research from the crater in the Yucatan Peninsula is helping researchers understand exactly what happened on the day that spelled doom for the dinosaurs (except birds) and began our chapter in the history of life.

Heating Up

Your image of the dinosaurs' last day might come from classroom posters that show a few clueless brontosauruses grazing on ferns while a flaming asteroid streaks across the sky, but that scene doesn't do justice to the object that slammed into Earth 66 million years ago. The infamous asteroid was no school bus-sized piece of rock. Officially known as the Chicxulub Impactor, the asteroid that doomed the dinosaurs was much, much bigger: between 6 and 50 miles (11 and 81 kilometers) in diameter. It struck the planet with enough force to cause Earth's crust to behave like a liquid, and the rock near the impact site literally melted. The drama of the collision's aftermath is frozen in time in the form of an undersea crater just off the Yucatan Peninsula in Mexico.

The first 24 hours after impact were hot, steamy confusion. The asteroid transferred a tremendous amount of energy to the Earth's crust when it landed in the Gulf of Mexico. Over the course of a few minutes, the force of the impact pushed rock out from the asteroid and then up into the sky like the splash from a cannonball at a pool party. The event forced rock from 6 miles below the surface outward and upward, forming a ring of peaks around the crater.

New research published in the journal PNAS is helping us all understand exactly how the events of the day unfolded. The biggest clues left behind in that massive and deadly crater are in its geology, which is why the team of researchers behind this study started by drilling in and around the crater to take samples and figure out what types of rock were where. Most of the rock they found in the crater had been created during the impact or forced into the crater as water displaced by the asteroid came rushing back.

But it's what the scientists didn't find — at least not in the crater — that makes the research so important. The normal rock in the area around the crater is full of the mineral sulfur. But when the researchers examined the samples taken from the crater itself, they found very little sulfur. It might seem like a mysterious problem, but this new data actually supports a long-standing theory that explains why this North American asteroid collision was so important to the history of the planet.

Cooling Off

It wasn't the tsunami, the wildfires, or the asteroid impact itself that spelled doom for the dinosaurs. It was the global cool-down that happened in the following weeks and years. What was behind the big chill? All the sulfur that was vaporized when the asteroid hit.

"The real killer has got to be atmospheric," said Sean Gulick, the researcher who led the study. "The only way you get a global mass extinction like this is an atmospheric effect."

Sulfur is incredibly effective at cooling the planet. It's why massive volcanic eruptions like the 1815 explosion of Mount Tambora can lead to months or years of chilly temperatures, and why some people are considering sulfur as the main ingredient in a drastic fix to global warming. When volcanoes or asteroid impacts send sulfur into the stratosphere, it combines with water to create tiny droplets that blanket the Earth and reflect sunlight back into space.

Plenty of dinosaurs died in the immediate aftermath, but it was that shift in Earth's climate that wiped out around 75 percent of life on the planet, including the dinosaurs. The collision kicked up so much dust — at least 325 billion metric tons of sulfur-bearing minerals — that the resulting global haze caused temperatures on the planet to plummet. The rapid change in climate caused environmental havoc and spurred the most recent global extinction (before the current one, that is).

The impact and its aftermath were bad news for most living things that existed at the time, but the demise of so many species was a boon for an insignificant class of animals that had been keeping their heads down for 150 million years. With dinosaurs and other cretaceous critters out of the way, mammals finally had an opportunity to thrive. The following 66 million years would witness a global explosion in the diversity and distribution of mammals, including us. All because of a chance meeting between a planet and some big rock from space.

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Dive deeper into the dawn of the dinos with "The Rise and Fall of the Dinosaurs: A New History of Their Lost World" by Steve Brusatte. The audiobook is free with an Audible trial. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Grant Currin October 9, 2019

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