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“But that’s just a short-term event from a relatively minor eruption, compared with Deccan,” Keller told me. A single Deccan eruption was “thousands of times larger” than Laki, she said. “And then you repeat that over and over again. For basically 350,000 years before the massive die-off.”

Laki released 3.3 cubic miles of lava; Deccan unleashed an estimated 720,000 cubic miles, eventually covering an area three times the size of France. It took us five hours of driving, an hour-and-a-half flight from Hyderabad to Pune, and another three hours in the car to trace the lava flows from some of their farthest, flattest reaches back to some of their highest points, in Mahabaleshwar, a vertiginous town crowded with honeymooners. Mountains of basalt 2.1 miles high—nearly twice as tall as the Grand Canyon is deep—extended as far as I could see. Even the geologists, who had visited the Deccan Traps multiple times before, gaped at the landscape.

“It’s mind-blowing,” Eddy said. “Every time.”

Keller, whose food poisoning had gone from bad to worse, made the van pull over so we could revisit an outcrop she’d sampled twice before, on previous trips. At the base of an undulating wall of black basalt, Keller ran her hand over a blood-colored layer of rock, bumpy and inflamed as a scab. Where we now stood was virtually within a blink of an eye of the mass extinction, she explained: Keller’s collaborators had dated this red layer and found that it was deposited tens of thousands of years before the extinction, just before Deccan’s largest and most lethal eruptions began.

“Shit hits the fan for the last 40,000 years,” Keller said. “The eruptions really took off. Huge. Absolutely huge. That’s when we have the longest lava flows on Earth, into the Bay of Bengal”—more than 600 miles away, practically the length of California.

A drawing that hangs over Keller’s desk at Princeton depicts her vision of this apocalypse, which was heavily informed by accounts of how Laki poisoned Iceland’s livestock. “I told [the artist], ‘Yellow foaming at the mouth!’ ” Keller recounted, delighted. In the illustration, dinosaurs, gurgling lime-green vomit, writhe on a hill spotted with flames and charred tree stumps; just behind them, a diagonal gash in the ground blazes with lava and spews dark, swirling clouds. According to Keller’s research, while Deccan’s lava flows would have devastated the Indian subcontinent, its release of ash, toxic elements (mercury, lead), and gases (sulfur, methane, fluorine, chlorine, carbon dioxide) would also have blown around the world, wreaking havoc globally.

As she sees it, the ash, mercury, and lead would have settled over habitats, poisoning creatures and their food supply. The belches of sulfur would have initially cooled the climate, then they would have drenched the Earth in acid rain, ravaging the oceans and destroying vegetation that land animals needed to survive. The combination of carbon dioxide and methane would have eventually raised temperatures on land by as much as 46 degrees Fahrenheit, further acidifying oceans and making them inhospitable to plankton and other forams. Once these microscopic creatures disappear from the base of the food chain, larger marine animals follow. “At that point, extinction is inevitable,” Keller said.

Rocks elsewhere in the world support the sequence of events Keller has discerned in the Deccan Traps. She and her collaborators have found evidence of climate change and skyrocketing mercury levels following the largest eruptions, and other researchers have documented elevated concentrations of sulfur and chlorine consistent with severe pollution by volcanic gases. Keller posits that even the iridium layers could be linked to Deccan’s eruptions, given that volcanic dust can carry high concentrations of the element.

She also sees Deccan’s fingerprints in the fossil record. The gradual decline of the forams—followed by their sudden, dramatic downfall—aligns with Deccan’s pattern of eruptions: Over several hundred thousand years, its volcanic activity stressed the environment, until its largest emissions dealt a final, devastating blow. The Earth’s flora and fauna did not show signs of recovery for more than 500,000 years afterward—a time period that coincides with Deccan’s ongoing belches. The volcano simmered long after most species had vanished, keeping the planet nearly uninhabitable.

6.

“Her conclusions are way off,” Jan Smit, the Dutch scientist, told me. After nearly 40 years of arguing, the two sides still cannot agree on fundamental facts. Smit and other impacters counter Keller’s scenario with a long list of rebuttals: The planet’s species went extinct “almost overnight,” Smit insists, too quickly to be caused by Deccan volcanism. India’s volcanoes hiccuped for hundreds of thousands of years, too weakly and for too long to be deadly, Keller’s critics contend. They argue that there is no evidence that species suffered while Deccan simmered, and that the biggest volcanic eruptions occurred after the extinction, too late to have been the catalyst. Besides, they add, new dating places the asteroid’s impact within 32,000 years of the annihilation—as close as a “gnat’s eyebrow,” says the geochronologist Paul Renne, who led the study.

Some scientists have attempted to find a middle ground between the two camps. A team at UC Berkeley, headed by Renne, has recently incorporated volcanism into the asteroid theory, proposing that Chicxulub’s collision unleashed earthquakes that in turn triggered Deccan’s most destructive pulses. But Keller rejects this hypothesis. “It’s impossible,” she told me. “They are trying to save the impact theory by modifying it.”

The greatest area of consensus between the volcanists and the impacters seems to be on what insults to sling. Both sides accuse the other of ignoring data. Keller says that her pro-impact colleagues “will not listen or discuss evidence that is contrary to what they believe”; Alan Hildebrand, a prominent impacter, says Keller “doesn’t look at all the evidence.” Each side dismisses the other as unscientific: “It’s not science. It sometimes seems to border on religious fervor, basically,” says Keller, whose work Smit calls “barely scientific.” Both sides contend that the other is so stubborn, the debate will be resolved only when the opposition croaks. “You don’t convince the old people about a new idea. You wait for them to die,” jokes Courtillot, the volcanism advocate, paraphrasing Max Planck. Smit agrees: “You just have to let them get extinct.”

All the squabbling raises a question: How will the public know when scientists have determined which scenario is right? It is tempting, but unreliable, to trust what appears to be the majority opinion. Forty-one co-authors signed on to a 2010 Science paper asserting that Chicxulub was, after all the evidence had been evaluated, conclusively to blame for the dinosaurs’ death. Case closed, again. Although some might consider this proof of consensus, dozens of geologists, paleontologists, and biologists wrote in to the journal contesting the paper’s methods and conclusions. Science is not done by vote.

Ultimately, consensus may be the wrong goal. Adrian Currie, a philosopher of science at Cambridge University, worries that the feverish competition in academia coupled with the need to curry favor with colleagues—in order to get published, get tenure, or get grant money—rewards timid research at the expense of maverick undertakings. He and others argue that controversy produces progress, pushing experts to take on more sophisticated questions. Some of Keller’s most outspoken critics told me that her naysaying has motivated their research. “She keeps us sharp, definitely,” Smit said. Though trading insults is not the mark of dispassionate scientific research, perhaps detached investigation is not ideal, either. It is passion, after all, that drives scientists to dig deeper, defy the majority, and hunt rocks in rural India for 12 hours at a stretch while suffering acute gastrointestinal distress.

7.

Keller’s attentiveness to the stories that rocks tell enables her to live concurrently in the past, present, and future. She was here, driving through Pune’s smog-filled mountains. The sight of their jagged outlines simultaneously transported her back in time 66 million years, to when the Indian subcontinent split apart, spewing gas, ash, and fire. That, in turn, evoked the eventual demise of the human species, which Keller argues will be triggered by forces similar to Deccan volcanism.

Keller fears that we are filling our environment with the same ingredients—sulfur, carbon dioxide, mercury, and more—that killed the dinosaurs and that, left unchecked, will catalyze another mass extinction, this one of our own devising. “You just replace Deccan volcanism’s effect with today’s fossil-fuel burning,” she told me. “It’s exactly the same.”

Keller sees a bleak future when she looks at our present. Oceans are acidifying. The climate is warming. Mercury levels are rising. Countless species are endangered and staring down extinction—much like the gradual, then rapid, downfall of the forams. Whether or not Deccan ultimately caused the mass extinction, its eruptions illuminate how our current environment may react to man-made pollutants. If Deccan was responsible, however, Keller’s theory casts our current actions in a terrifying light. (Not to be outdone, impacters recently highlighted the Chicxulub asteroid’s relevance to the present day in a paper for Science, arguing that the asteroid injected enough carbon dioxide into the atmosphere to cause 100,000 years of global warming.)

Source : https://www.theatlantic.com/magazine/archive/2018/09/dinosaur-extinction-debate/565769/

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