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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.

THE SMOKING CANNON

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 been subducted, where one tectonic plate slides beneath another—which would have prevented scientists from discovering samples. When Kring and his team looked at the samples they were able to take, there was shock quartz in one of the layers. “The minute you see shock quartz, that is absolutely, categorically diagnostic of impact,” says Kring. “You know that’s not a buried volcano. It’s an impact crater, and that’s your eureka moment.”

When Kring found the Chicxulub Crater, it finally provided scientific evidence for the Impact Mass Extinction Hypothesis. Developed by physicist Luis Alvarez, the theory proposes that the extinction of the dinosaurs was caused by a catastrophic asteroid impact with the Earth. The theory made a lot of sense. An impact of such magnitude would certainly leave a mark, after all. The dominant alternative hypothesis was that overdrive volcanic activity caused catastrophic climate change, leaving the dinosaurs in a bad spot. Finding an impact crater of this magnitude, scientist Gene Shoemaker would later tell Time magazine, was “the smoking cannon.”

The discovery that impact cratering is not only a geological process but a biological one caused a major shift in scientific thinking during the 20th century. The idea that you could have catastrophic events completely change the evolutionary path of the planet was staggering in its implication. Impact Mass Extinction Hypothesis, and the subsequent discovery of Chicxulub Crater, were argued by some as fundamentally more important, and bigger shifts in the tenets of geology, than learning about continental drift.

THE ORIGIN OF LIFE ON EARTH

When a fireball hit the Earth 66 million years ago, the Mesozoic Era (the Age of Reptiles) ended and the Cenozoic―the Age of Mammals―began. One second before the strike, in the part of the sea that must have had a dark shadow pooling rapidly outward as the asteroid approached, 50-foot sea monsters called mosasaurs swarmed and devoured fish and mollusks. One second after the asteroid hit, those mosasaurs were gone, and chunks of the planet were blown thousands of miles in every direction. Every continent on Earth was devastated in the blink of a geologic eye. A 300-foot tsunami washed across North and South America. The Sun was blotted out. Plants relying on photosynthesis declined or went extinct. If you were a dinosaur who couldn’t fly, you were done for. Seventy-five percent of all species of life were obliterated.

But bad as that sounds, approximately 4 billion years ago, an impact likely larger even than Chicxulub would have vaporized the sea and created a rock vapor atmosphere for thousands of years. The impacts would have produced vast subsurface hydrothermal (hot water) systems that were perfect crucibles for prebiotic chemistry. The new core samples taken from deep in Chicxulub provide physical evidence of this theory. The samples are fractured and permeable—perfect for the circulation of hot fluid. Moreover, they also have signatures of hot fluids and altered rock and hydrothermal minerals.

The hydrothermal systems caused by an asteroid collision may have lasted for as long as 2.3 million years. This is critical, because life needs time to establish itself and evolve. Those systems would have evolved into perfect habitats for the evolution of life.

Kring's Chicxulub research suggests that these are the types of places life evolved in early Earth history. Further research will look at the analysis of rock samples for radiometric signatures, to try to determine how long that system persisted. It's also given rise to a new theory: the Impact Origin of Life Hypothesis.

This impact origin of life theory is not necessarily limited to Earth, as research from Susanne Schwenzer, Oleg Abramov, and others suggest. “It is generically translatable,” says Kring. “Impact cratering, as it turns out, is an important heat engine for planetary bodies. Impact events on icy satellites can melt icy shells and produce seeds. You need liquid water for life. That may have had a role of life in our outer system.” This also applies to extrasolar planetary systems.

Whether life originated anywhere beyond Earth is still to be determined, but this is a big step toward understanding what conditions to look for. You can be sure when it’s announced, that scientist will certainly play to a standing-room-only crowd yet again.

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Space
Here's Where You Can Watch a Livestream of Cassini's Final Moments
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It's been a road trip like no other. After seven years and 2.2 billion miles, the NASA orbiter Cassini finally arrived at the Saturn system on June 30, 2004. Ever since, it's been capturing and transmitting valuable data about the distant environment. From sending the Huygens probe to land on the moon Titan to witnessing hurricanes on both of the planet's poles, Cassini has informed more than 3000 scientific papers.

It's been as impressive a mission as any spacecraft has ever undertaken. And tomorrow, Cassini will perform one last feat: sacrificing itself to Saturn's intense atmosphere. Project scientists are deliberately plunging it into the planet in order to secure just a little more data—and to keep the spacecraft, which is running low on fuel, from one day colliding with a Saturnian moon that might harbor life.

Because it won't have time to store anything on its hard drive, Cassini will livestream its blaze of glory via NASA. The information will be composed mostly of measurements, since pictures would take too long to send. Instead, we'll get data about Saturn's magnetic field and the composition of its dust and gas.

"As we fly through the atmosphere, we are able to literally scoop up some molecules, and from those we can figure out the ground truth in Saturn’s atmosphere," Scott Edgington, a Cassini project scientist, told New Scientist. "Just like almost everything else in this mission, I expect to be completely surprised."

The action will kick off at 7 a.m. EDT on Friday, September 15. Scientists expect to say goodbye to Cassini less than an hour later. 

While you wait for Cassini's grand finale, you can check out some essential facts we've rounded up from Saturn experts. And keep your eyes peeled for a full recap of Cassini’s historic journey: Mental Floss will be in the control room at the Jet Propulsion Laboratory in Pasadena, California, to offer a firsthand account of the craft's final moments in space. 

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Big Questions
What Are the Northern Lights?
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Over the centuries, many have gazed up at one of the Earth’s most fascinatingly beautiful natural wonders: the Northern Lights. In the past couple of weeks, some lucky American stargazers have gotten the chance to see them from their very own backyards—and could again this week, according to Thrillist. But what are they?

Before science was able to get a read on what exactly was happening in the night sky, ancient tribes had their own theories for what caused the jaw-dropping light show. Many early beliefs had roots in religion, such as that the light was a pathway souls traveled to reach heaven (Eskimo tribes) or that the light was an eternal battle of dead warriors (Middle-Age Europe). Early researchers were a bit more reasonable in their approximations, and most surrounded the idea of the reflection of sunlight off the ice caps. In 1619, Galileo Galilei named the lights the aurora borealis after Aurora, the Roman goddess of morning, after concluding they were a product of sunlight reflecting from the atmosphere.

Today, scientists have come to the general agreement that the lights are caused by the collision of electrically charged solar particles and atoms from our atmosphere. The energy from the collisions is released as light, and the reason it happens around the poles is because that's where the Earth’s magnetic field is the strongest. In 2008, a team at UCLA concluded that “when two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat. Energy is released, and the plasma is accelerated, producing accelerated electrons.”

"Our data show clearly and for the first time that magnetic reconnection is the trigger," said Vassilis Angelopoulos, a UCLA professor of Earth and Space Sciences. "Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond. We are providing the evidence that this is happening."

The best time to see the Northern Lights is during the winter, due to the Earth’s position in relation to the sun (shorter days means darker night skies). And by the way, it’s not just the North Pole that puts on a show—there are Southern Lights, too. There are also aurora borealis on other planets—including Mars—so rest assured that future generations born “abroad” will not miss out on this spectacular feat of nature.

Haven’t seen them yet? Traditionally, the best places to catch a glimpse of the Northern Lights are in Iceland, Sweden, Norway, Finland, Greenland, northern Canada, and Alaska. Maybe you'll get lucky this week and sneak a peek from your very own window. Check out Aurorasaurus for regular updates on where they are showing.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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