UC Berkeley Geophysicists: Did Dinosaur-Killing Asteroid Trigger Largest Lava Flows On Earth?
- Last Updated: Sunday, 03 May 2015 04:22
April 2015 - BERKELEY - By Robert Sanders - The asteroid that slammed into the ocean off Mexico 66 million years ago and killed off the dinosaurs probably rang the Earth like a bell, triggering volcanic eruptions around the globe that may have contributed to the devastation, according to a team of UC Berkeley geophysicists.
(Left) Mark Richards sampling a weathered zone between two lava flows of the Deccan Traps, near the town of Mahabeleshwar, India. These zones, locally called “red boles,” may represent periods of time elapsed between the eruption of successive gigantic lava flows. (Paul Renne photo)
Specifically, the researchers argue that the impact likely triggered most of the immense eruptions of lava in India known as the Deccan Traps, explaining the “uncomfortably close” coincidence between the Deccan Traps eruptions and the impact, which has always cast doubt on the theory that the asteroid was the sole cause of the end-Cretaceous mass extinction.
“If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan … the chances of that occurring at random are minuscule,” said team leader Mark Richards, UC Berkeley professor of earth and planetary science. “It’s not a very credible coincidence.”
Richards and his colleagues marshal evidence for their theory that the impact reignited the Deccan flood lavas in a paper to be published in The Geological Society of America Bulletin, available online in advance of publication.
While the Deccan lava flows, which started before the impact but erupted for several hundred thousand years after re-ignition, probably spewed immense amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, it’s still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs, Richards said.
“This connection between the impact and the Deccan lava flows is a great story and might even be true, but it doesn’t yet take us closer to understanding what actually killed the dinosaurs and the ‘forams,’” he said, referring to tiny sea creatures called foraminifera, many of which disappeared from the fossil record virtually overnight at the boundary between the Cretaceous and Tertiary periods, called the KT boundary. The disappearance of the landscape-dominating dinosaurs is widely credited with ushering in the age of mammals, eventually including humans.
He stresses that his proposal differs from an earlier hypothesis that the energy of the impact was focused around Earth to a spot directly opposite, or antipodal, to the impact, triggering the eruption of the Deccan Traps. The “antipodal focusing” theory died when the impact crater, called Chicxulub, was found off the Yucatán coast of Mexico, which is about 5,000 kilometers from the antipode of the Deccan traps.
Flood basalts
Richards proposed in 1989 that plumes of hot rock, called “plume heads,” rise through Earth’s mantle every 20-30 million years and generate huge lava flows, called flood basalts, like the Deccan Traps. It struck him as more than coincidence that the last four of the six known mass extinctions of life occurred at the same time as one of these massive eruptions.
(Right) Illustration of a hot mantle plume “head” pancaked beneath the Indian Plate. The theory by Richards and his colleagues suggests that existing magma within this plume head was mobilized by strong seismic shaking from the Chicxulub asteroid impact, resulting in the largest of the Deccan Traps flood basalt eruptions.
“Paul Renne’s group at Berkeley showed years ago that the Central Atlantic Magmatic Province is associated with the mass extinction at the Triassic/Jurassic boundary 200 million years ago, and the Siberian Traps are associated with the end Permian extinction 250 million years ago, and now we also know that a big volcanic eruption in China called the Emeishan Traps is associated with the end-Guadalupian extinction 260 million years ago,” Richards said. “Then you have the Deccan eruptions – including the largest mapped lava flows on Earth – occurring 66 million years ago coincident with the KT mass extinction. So what really happened at the KT boundary?”
Richards teamed up with experts in many areas to try to discover faults with his radical idea that the impact triggered the Deccan eruptions, but instead came up with supporting evidence. Paul Renne, a professor in residence in the UC Berkeley Department of Earth and Planetary Science and director of the Berkeley Geochronology Center, re-dated the asteroid impact and mass extinction two years ago and found them essentially simultaneous, but also within approximately 100,000 years of the largest Deccan eruptions, referred to as the Wai subgroup flows, which produced about 70 percent of the lavas that now stretch across the Indian subcontinent from Mumbai to Kolkata.
Michael Manga, a professor in the same department, has shown over the past decade that large earthquakes – equivalent to Japan’s 9.0 Tohoku quake in 2011 – can trigger nearby volcanic eruptions. Richards calculates that the asteroid that created the Chicxulub crater might have generated the equivalent of a magnitude 9 or larger earthquake everywhere on Earth, sufficient to ignite the Deccan flood basalts and perhaps eruptions many places around the globe, including at mid-ocean ridges.
“It’s inconceivable that the impact could have melted a whole lot of rock away from the impact site itself, but if you had a system that already had magma and you gave it a little extra kick, it could produce a big eruption,” Manga said.
Similarly, Deccan lava from before the impact is chemically different from that after the impact, indicating a faster rise to the surface after the impact, while the pattern of dikes from which the supercharged lava flowed – “like cracks in a soufflé,” Renne said – are more randomly oriented post-impact.
“There is a profound break in the style of eruptions and the volume and composition of the eruptions,” said Renne. “The whole question is, ‘Is that discontinuity synchronous with the impact?’”
Reawakened volcanism
Richards, Renne and graduate student Courtney Sprain, along with Deccan volcanology experts Steven Self and Loÿc Vanderkluysen, visited India in April 2014 to obtain lava samples for dating, and noticed that there are pronounced weathering surfaces, or terraces, marking the onset of the huge Wai subgroup flows. Geological evidence suggests that these terraces may signal a period of quiescence in Deccan volcanism prior to the Chicxulub impact. Apparently never before noticed, these terraces are part of the western Ghats, a mountain chain named after the Hindu word for steps.
(Left) Photograph of part of the main stack of 66 million year old Deccan Traps lava flows near the city of Mahabaleshwar, India. The entire volume of the Deccan Traps could have covered an area as large as the state of California in a mile deep pile of lava flows.(Mark Richards photo)
“This was an existing massive volcanic system that had been there probably several million years, and the impact gave this thing a shake and it mobilized a huge amount of magma over a short amount of time,” Richards said. “The beauty of this theory is that it is very testable, because it predicts that you should have the impact and the beginning of the extinction, and within 100,000 years or so you should have these massive eruptions coming out, which is about how long it might take for the magma to reach the surface.”
Since the team’s paper was accepted for publication, a group from Princeton University published new radioisotopic dates for the Deccan Traps lavas that are consistent with these predictions. Renne and Sprain at UC Berkeley also have preliminary, unpublished dates for the Deccan lavas that could help solidify Richards’ theory, Renne said.
Co-authors of the paper, in addition to Richards, Renne, Manga and Sprain, are Walter Alvarez, a UC Berkeley professor emeritus of earth and planetary science and the co-originator of the dinosaur-killing asteroid theory; Stephen Self, an adjunct professor in the same department at UC Berkeley; Leif Karlstrom of the University of Oregon; Jan Smit of Vrije Universeit in Amsterdam, the Netherlands; Loÿc Vanderkluysen of Drexel University in Philadelphia, Pennsylvania; and Sally A. Gibson of the University of Cambridge in the United Kingdom.
UC Berkeley Geophysicists: Did Dinosaur-Killing Asteroid Trigger Largest Lava Flows On Earth?
Did Dinosaur-Killer Asteroid Ignite Massive Volcanic Eruptions? (Weekend Feature)
The Death of the Dinosaurs
By PETER BRANNENJAN. 31, 2015
BOSTON — BY now the image of the demise of the dinosaurs has become iconic: a luckless tyrannosaur looking over its shoulder as a colossal fireball from heaven bears down on the horizon, the monster’s death by vaporization imminent.
Hanging above the desk of the Princeton geologist
Gerta Keller, though, is a different artist’s depiction. This time it’s a pair of tyrannosaurs — still doomed — but not by an errant space rock. In this picture they’re writhing on the ground in a withered landscape as eruptions from volcanoes and fissures in the ground tear the earth apart.
These dinosaurs were killed not by the lava itself, but by the environmental catastrophe unleashed by the volcanic gases. It was an end time of global warming, acid rain and acidifying oceans that might sound familiar today as a vast body of scientific research warns us of our own developing ecological crisis.
The difference between these two pictures represents one of the most acrimonious battles in science.
The fireball image was born in 1980 when the father-son team of Luis and Walter Alvarez at the University of California, Berkeley, dropped an asteroid on the unsuspecting fields of geology and paleontology, neatly explaining away one of the most vexing problems in science — the death of the dinosaurs.
Their salvo landed in the journal Science in a paper still regarded with a remember-where-you-were-when-you-first-read-it reverence. In the paper, the Alvarezes pointed to traces of extraterrestrial dust in the geologic record coincident with the extinction, a finding that was later buoyed by the discovery of a 110-mile impact
crater centered in Chicxulub, Mexico.
The theory — positing a day of hellfire and months of darkness as dust and smoke from the impact and fires blotted out the sun — was as sensational as theories get. Professional and personal relationships were strained and sometimes broken as scientists hitched their careers to the flashy new theory, or clung to earthbound causes for the mass extinction.
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In the past few decades, as a consensus has calcified around the asteroid theory, perhaps no one has endured more ostracism than Dr. Keller, who has long pointed to enormous floods of lava in India, called the
Deccan Traps, as an alternate explanation for the demise of three-quarters of all animal and plant life. But her sojourn in the academic wilderness may be ending as more evidence emerges for the deadliness of these volcanoes.
The planet has endured five major mass extinctions in which most of its fauna was wiped away in a geologic eye blink. They are known as the Big Five. Some, like the
End-Permian mass extinction, 252 million years ago, were even worse than the catastrophe that wiped out the dinosaurs.
These events had long been mysterious; some 19th-century natural philosophers viewed the reboot of the biosphere that followed them as evidence of separate acts of divine creation. With the introduction of the Alvarez hypothesis, there was now a plausible and testable mechanism for these apocalypses. Geologists set out across the planet, scouring the fossil record for evidence of asteroid impacts at each of the other crises in Earth’s history. They came up empty.
Plausible candidates, like the 62-mile-wide
Manicouagan crater in Quebec, now a circular system of lakes, seemed to fit the bill. The asteroid that created it was large enough, computer models showed, to have wiped out up to a third of life on Earth. But when the crater was dated, there was no evidence of such a catastrophe.
Other enormous impacts, like the one that created the Chesapeake Bay 35 million years ago, left no discernible echoes in the fossil record, either.
While evidence for asteroids at the other mass-extinction boundaries was hard to come by, researchers did find a coincidence in time with continent-flooding cascades of lava on a scale unimaginable today.
How these lava flows, known as large igneous provinces, rendered their destruction is an active area of study, but some clear signatures appear at many of the episodes, including huge injections of carbon dioxide into the atmosphere, intense global warming and ocean acidification as carbon dioxide was absorbed by the seas.
In Siberia, one such volcanic province spewed so much carbon into the air that parts of the ocean reached — as one paleontologist put it — the temperature of “hot soup.” Seas became more acidic, as they are becoming today, and calcifying animals like corals died en masse, along with 96 percent of ocean life during the End-Permian extinction.
We now know, through the dating of the Palisades across from New York City, that 50 million years later, virtually the same thing happened at the end of the Triassic, when lava gushed from the seams of the supercontinent Pangaea as it tore apart.
That brings us, 135 million years later, to the most recent of the Big Five: the extinction of the nonbird dinosaurs, along with much else that was living at the time. It has long been known that huge areas of western India were being smothered in lava, in some places more than a mile deep, close in time to the extinction. Asteroid proponents have long dismissed this volcanism as an irritating coincidence — the smoking gun having already been placed satisfactorily in the hands of a culprit from outer space.
But Dr. Keller’s team, led by her Princeton colleague Blair Schoene, recently dated the Indian lava flows with the same precise radiometric dating techniques that have recently tied other massive lava flows to mass extinctions. The most destructive phase of volcanism, the scientists found, took place over less than 750,000 years, a geologically brief span, and overlapped the extinction.
Dr. Keller points to rocks in Texas, Tunisia and elsewhere that indicate warming episodes of at least 7 degrees Fahrenheit in under 10,000 years, with acidifying oceans that killed all but the hardiest life-forms, which then thrived for millenniums.
Still, few are ready to demote the role of the dinosaurs’ asteroid, which created a crater larger than any found in the half-billion-year history of animal life. Some experts still contend that it was the lone killer. But many now lean toward a one-two punch of a planet weakened by volcanoes and then crippled by the asteroid. Or vice versa. Or perhaps the coincidence in time between the asteroid, the volcanoes and the extinction, is not a coincidence at all.
At a meeting in October of the Geological Society of America, Walter Alvarez patiently looked on as Dr. Keller presented her work dismissing his asteroid theory. When it was time for Professor Alvarez’s Berkeley collaborator, Mark Richards, to present his team’s paper, Dr. Richards admitted the destructive potential of the Deccan Traps and called their proximity in the fossil record to the asteroid “the 8,000-pound gorilla in the room.” Perhaps, he said, there was even a causal link between the asteroid — which induced a magnitude 12 earthquake — and the most destructive period of Indian volcanism.
As another author of the paper, Paul Renne of Berkeley, explained to me, the asteroid might have perturbed Earth’s mantle and turned an already disastrous volcanic episode in India apocalyptic. The work borders on speculative at this point and is far from an endorsement of Dr. Keller’s conclusions, but it is still a fragile olive branch in a field where few have been extended in recent decades.
“It may be that Chicxulub was the gun and the Deccan Traps were the bullet,” Dr. Renne said.
http://www.nytimes.com/2015/02/01/opinion/sunday/the-death-of-the-dinosaurs.html?_r=0
