Impact event

The Fireball That Killed the Dinosaurs Could Help Us Find Life on Other Planets

When David Kring of the University of Arizona gave a presentation at the Lunar and Planetary Science Conference in 1991, he didn’t expect a packed crowd for his talk on the petrology of the Chicxulub Structure in the Yucatan, Mexico. Normally, Kring knew, impact-cratering sessions were presented in the smallest room—the miserable Room D, a shoebox on the second floor. But the magnitude of his announcement attracted scientists across fields and disciplines, so he was bumped up to the main room.

Kring had been investigating a place called the Yucatán-6 borehole, and he and his team had discovered shock quartz and impact melt fragments in two thumb-sized bits of rock that were over half a mile beneath the surface of the Earth. This was evidence that the hole, thought for a very long time to be a volcanic center, was actually an impact structure. And not just any “impact structure,” and not just any crater―but the crater of all craters on Earth. The one behind the death of the dinosaurs 66 million years ago.

Last year, Kring was part of an expedition in which scientists drilled into Chicxulub to investigate how the disastrous collision of fireball and Earth that killed the dinosaurs also created the conditions for life to begin anew. Last month, Kring and his colleagues returned to the Lunar and Planetary Science Conference to present their findings from the new core samples they took on that expedition. The results provide new clues about how life may have begun on Earth about 4 billion years ago—and point us towards how and where we can look for life across the universe.


Back in the early 1990s, Kring knew what he was looking for—a crater of the size and magnitude that would provide evidence of catastrophic extinction—but he didn’t know where to look. “It was a race to find the impact site,” Kring tells mental_floss, “and we had made a discovery of this very thick impact ejecta deposit in Haiti, which pointed us to [the Yucatan].”

Impact ejecta is what’s blasted from the Earth or other body when a meteor crashes into it. In this case, a giant chunk of the Earth was blown a thousand miles away. Until the Haiti discovery, people were looking all over the planet for the crater. But now they had a target region. Meanwhile, Petroleos Mexicanos, an oil company, had drilled down into what they thought was a “geophysical anomaly” in the Yucatan―a salt dome, maybe, where there might be oil. That’s when Kring and his colleagues re-examined samples collected from the site and realized there were features consistent with an impact.

That the Yucatan site was still intact to be found wasn’t a given. In the last 65 million years, half of the seafloor has…

Readers dispute starfishes’ water-swirling abilities

Dinosaurs and other creatures were largely wiped out 66 million years ago from an asteroid impact, volcanic eruptions or maybe a mix of the two, Thomas Sumner reported in “Devastation detectives” (SN: 2/4/17, p. 16), in the Science News special report “Dino Doomsday.”

Online reader Mike van Horn wondered if the timing of the volcanic eruptions, which happened for hundreds of thousands of years before and after the asteroid impact, could have allowed marine organisms to adapt to increasingly acidic oceans.

Scientists don’t know if bouts of volcanic eruptions helped marine critters survive the harsh post-impact environment. But studies of ocean acidification’s effects on marine organisms living today hint that adaptation may not have been viable, Sumner says. In a recent experiment, armor-plated phytoplankton regained their shell-making abilities after researchers dunked them in acidified water. But those gains disappeared after further exposure (SN: 8/6/16, p. 8).

Swirling controversy

Starfish larvae use hairlike cilia to stir up whorls of water, called eddies, and suck in prey, Emily Conover reported in “Baby starfish on the hunt whip up whirlpools” (SN: 2/4/17, p. 14).

Reader George von Dassow disputes the reported finding. “Unfortunately, [the researchers’] work is based on a well-documented and well-understood artifact, which biologists who study the behavior of microorganisms often work hard to avoid,” wrote von Dassow, a developmental biologist at the University…