Geologists Find Clues In Crater Left By Dinosaur-Killing Asteroid

May 6, 2016
Originally published on May 17, 2016 10:40 pm

Scientists have had a literal breakthrough off the coast of Mexico.

After weeks of drilling from an offshore platform in the Gulf of Mexico, they have reached rocks left over from the day the Earth was hit by a killer asteroid.

The cataclysm is believed to have wiped out the dinosaurs. "This was probably the most important event in the last 100 million years," says Joanna Morgan, a geophysicist at Imperial College in London and a leader of the expedition.

Since the 1980s, researchers have known about the impact site, located near the present-day Yucatan Peninsula. Known as Chicxulub, the crater is approximately 125 miles across. It was created when an asteroid the size of Staten Island, N.Y., struck Earth around 66 million years ago. The initial explosion from the impact would have made a nuclear bomb look like a firecracker. The searing heat started wildfires many hundreds of miles away.

After that, came an unscheduled winter. Sulfur, ash and debris clouded the sky. Darkness fell and, for a while, Earth was not itself.

"I think it was a bad few months, really," Morgan says.

That's an understatement: Scientists believe 75 percent of life went extinct during this dark chapter in Earth's history, including the dinosaurs.

Researchers have sampled Chicxulub before, but this expedition by the European Consortium for Ocean Research Drilling precisely targets a key part of the crater yet to be studied: a ring of mountains left by the asteroid. This "peak ring" is a fundamental feature of the strike and should tell researchers much more about it, says Sean Gulick, a geophysicist at the University of Texas at Austin, who co-leads the team with Morgan.

For weeks, they've been drilling — and going back in time. Each layer of rock they pass through is connected to a part of Earth's history.

"We went through a remarkable amount of the post-impact world. All the way into the Eocene times — so between 50 and 55 million years ago," Gulick says.

The rocks they've pulled out show how life began to recover after the cataclysm, Gulick says. "We've got all these limestones and rocks that contain the fossils from the world after the impact, all the things that evolved from the few organisms that survived."

The research team finally reached the top of the peak ring this week. It appears to be a thick layer of broken, melted rock just beneath a layer of sandstone that may be the leavings of a huge tsunami that was triggered when the asteroid struck.

Gulick thinks the rocks hold clues. For example, if any microscopic organisms survived near the site of the strike, their fossils might be in these samples. In June, the rock cores will be sent back to a lab in Germany for further study.

The asteroid strike marked the end of an era. But the creatures that made it through that catastrophe went on to shape the world again, says Morgan.

"The mammals survived," she says. "And that led on to our own evolution."

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ROBERT SIEGEL, HOST:

Scientists have had a literal breakthrough off the coast of Mexico. For weeks, they have been drilling into an underwater crater - the site of the asteroid impact that's believed to have killed the dinosaurs. As NPR's Geoff Brumfield reports, they've now hit the rocks that were scorched on the day of that impact.

GEOFF BRUMFIELD, BYLINE: I contacted the research team on their offshore platform, where they were drilling to the rock. Actually, when I called, they were dealing with some mechanical problems. Their drill bit had just died.

SEAN GULICK: It's been - well, I would say an emotional roller coaster (laughter).

BRUMFIEL: Sean Gulick is a researcher at the University of Texas at Austin who's helping to leave this expedition. To replace the bit, they had to pull it out from the hole, which is over 2000 feet deep and at the bottom of the ocean.

GULICK: You know, this is a little more laborious than just popping out a drill bit in the shop and putting a new one in.

BRUMFIEL: This has been Gulick's life for the past three weeks. He and the rest of the scientific team are burrowing through 66 million years of rock to recover samples from a single day that changed Earth's history forever. Joanna Morgan is from Imperial College in London.

JOANNA MORGAN: This was probably the most important event in the last hundred-million years.

BRUMFIEL: Morgan is the other scientist in charge on the platform. She runs the 12-hour night shift. Gulick runs the day. Long ago, very close to this now empty patch of ocean, an asteroid the size of Staten Island came hurtling in from space. It slammed into the sea near the site. The initial explosion would made a nuclear bomb look like a firecracker. The heat was searing.

MORGAN: We'd expect that to burn everything up and cause wildfires on land.

BRUMFIEL: After that came an unscheduled winter. Sulfur, ash, debris all clouded the sky. Darkness fell. And for a while, the Earth was not itself.

MORGAN: It would have been a very sort of dark, cold place. I think it was a bad few months, really (laughter).

BRUMFIEL: That's an understatement. Scientists believe 75 percent of life went extinct, including the dinosaurs. Researchers have known for decades the asteroid hit near modern-day Mexico. This expedition precisely targets a key part of the crater - a ring of mountains left by the asteroid's impact. With the drill bit fixed, it's back to work. As they keep digging, they are literally going back in time. Each layer of rock they pass through is connected to a part of Earth's history.

GULICK: We went through a remarkable amount of the post-impact world, all the way into the Eocene time, so between 50 and 55 million years ago.

BRUMFIEL: Closer and closer to the time of the asteroid. The rocks they've pulled out already show how life began to recover from the cataclysm.

GULICK: So we've got all these limestones and rocks that contain the fossils from the world of after the impact - all the things that evolved from the few organisms that survived.

BRUMFIEL: And then, just this week, they finally found it - a thick layer of broken, melted rock.

GULICK: What we see is this massive layer that is the event, right, that is the processes that happened on the day of the impact, would be the way to think about it.

BRUMFIEL: What exactly did happen? How did this event change our planet? Gulick thinks the rocks hold clues. For example, at some point, life returned to the crater. These samples might tell researchers how soon it came back and what it looked like. I asked Gulick - does drilling into the crypt from this apocalypse freak him out? He said, nah, not really.

GULICK: It's exciting to us. You know, I guess it's maybe a difference if you watch, you know, a science-fiction movie whether you're freaked out by the concept of something that is beyond us, or if, in fact, you're intrigued by the concept of something as phenomenal as, say, an impact that can do this much destruction to the Earth.

BRUMFIEL: The drilling will continue through June. Then, the samples go to the lab, where scientists hope they will yield important details about this one very bad day in Earth's history. Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.