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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 Brumfiel reports, they've now hit the rocks that were scorched on the day of that impact.
GEOFF BRUMFIEL, 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.
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