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  • richardmitnick 1:00 pm on January 17, 2020 Permalink | Reply
    Tags: "In death of dinosaurs it was all about the asteroid — not volcanoes", , Cretaceous-Paleogene extinction event 66 million years ago, , , , , Site of the asteroid strike 66 million years ago is an impact crater buried underneath the Yucatán Peninsula in Mexico. The asteroid doomed the dinosaurs., The Chicxulub crater, The Deccan Traps, ,   

    From Yale University: “In death of dinosaurs, it was all about the asteroid — not volcanoes” 

    From Yale University

    January 16, 2020
    Jim Shelton

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    (© stock.adobe.com)

    Volcanic activity did not play a direct role in the mass extinction event that killed the dinosaurs, according to an international, Yale-led team of researchers. It was all about the asteroid.

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    K-T boundary (red arrow) along Interstate 25, Raton Pass, Colorado. The Cretaceous–Paleogene boundary of 66 million years ago, marking the temporal border between the Cretaceous and Paleogene periods of geological time, was identified by a thin stratum of iridium-rich clay. During the 1970s, Walter Alvarez was doing geologic research in central Italy. There he had located an outcrop on the walls of a gorge whose limestone layers included strata both above and below the Cretaceous–Paleogene boundary. Exactly at the boundary is a thin layer of clay. Walter told his father Luis that the layer marked where the dinosaurs and much else became extinct and that nobody knew why, or what the clay was about — it was a big mystery and he intended to solve it. A team led by Luis Alvarez proposed in 1980 an extraterrestrial origin for this iridium, attributing it to an asteroid or comet impact. Their theory, known as the Alvarez hypothesis, is now widely accepted to explain the extinction of the non-avian dinosaurs. A large buried impact crater structure with an estimated age of about 66 million years was later identified under what is now the Yucatán Peninsula (the Chicxulub crater)

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    The Chicxulub crater is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. It was formed by a large asteroid or comet about 11 to 81 kilometers in diameter, the Chicxulub impactor, striking the Earth, and causing the dinosaur extinction.

    In a break from a number of other recent studies, Yale assistant professor of geology & geophysics Pincelli Hull and her colleagues argue in a new research paper in Science that environmental impacts from massive volcanic eruptions in India in the region known as the Deccan Traps happened well before the Cretaceous-Paleogene extinction event 66 million years ago and therefore did not contribute to the mass extinction.

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    Deccan Traps at Ajanta Caves. Shaikh Munir

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    The hardened lava flows of the Deccan Traps, in western India. Gerta Keller

    Most scientists acknowledge that the mass extinction event, also known as K-Pg, occurred after an asteroid slammed into Earth. Some researchers also have focused on the role of volcanoes in K-Pg due to indications that volcanic activity happened around the same time.

    “Volcanoes can drive mass extinctions because they release lots of gases, like SO2 and CO2, that can alter the climate and acidify the world,” said Hull, lead author of the new study. “But recent work has focused on the timing of lava eruption rather than gas release.”

    To pinpoint the timing of volcanic gas emission, Hull and her colleagues compared global temperature change and the carbon isotopes (an isotope is an atom with a higher or lower number of neutrons than normal) from marine fossils with models of the climatic effect of CO2 release. They concluded that most of the gas release happened well before the asteroid impact — and that the asteroid was the sole driver of extinction.

    “Volcanic activity in the late Cretaceous caused a gradual global warming event of about two degrees, but not mass extinction,” said former Yale researcher Michael Henehan, who compiled the temperature records for the study. “A number of species moved toward the North and South poles but moved back well before the asteroid impact.”

    Added Hull, “A lot of people have speculated that volcanoes mattered to K-Pg, and we’re saying, ‘No, they didn’t.’”

    Recent work on the Deccan Traps, in India, has also pointed to massive eruptions in the immediate aftermath of the K-Pg mass extinction. These results have puzzled scientists because there is no warming event to match. The new study suggests an answer to this puzzle, as well.

    “The K-Pg extinction was a mass extinction and this profoundly altered the global carbon cycle,” said Yale postdoctoral associate Donald Penman, the study’s modeler. “Our results show that these changes would allow the ocean to absorb an enormous amount of CO2 on long time scales — perhaps hiding the warming effects of volcanism in the aftermath of the event.”

    German researcher André Bornemann was co-lead author of the study. Yale researcher Ellen Thomas was a co-author of the study, along with additional researchers from institutions in Germany, the United Kingdom, France, Spain, Japan, Denmark, and the United States.

    The International Ocean Discovery Program, the National Science Foundation, and Yale University helped fund the research.

    See the full article here .

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    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

     
  • richardmitnick 10:34 am on February 22, 2019 Permalink | Reply
    Tags: "Did volcanic eruptions help kill off the dinosaurs?", A large impact crater in the Gulf of Mexico, A massive asteroid strike 66 million years ago that unleashed towering tsunamis and blotted out the sun with ash causing a plunge in global temperatures, Across what is India today countless volcanic seams opened in the ground releasing a flood of lava resembling last year’s eruptions in Hawaii—except across an area the size of Texas, , Over the course of 1 million years the greenhouse gases from these eruptions could have raised global temperatures and poisoned the oceans leaving life in a perilous state before the asteroid impact, , Some 400000 years before the impact the planet gradually warmed by some 5°C only to plunge in temperature right before the mass extinction, The Deccan Traps,   

    From Science Magazine: “Did volcanic eruptions help kill off the dinosaurs?” 

    AAAS
    From Science Magazine

    Feb. 21, 2019
    Paul Voosen

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    The hardened lava flows of the Deccan Traps, in western India, may have played a role in the demise of the dinosaurs. Gerta Keller

    What killed off the dinosaurs? The answer has seemed relatively simple since the discovery a few decades ago of a large impact crater in the Gulf of Mexico. It pointed to a massive asteroid strike 66 million years ago that unleashed towering tsunamis and blotted out the sun with ash, causing a plunge in global temperatures.

    But the asteroid wasn’t the only catastrophe to wallop the planet around this time. Across what is India today, countless volcanic seams opened in the ground, releasing a flood of lava resembling last year’s eruptions in Hawaii—except across an area the size of Texas. Over the course of 1 million years, the greenhouse gases from these eruptions could have raised global temperatures and poisoned the oceans, leaving life in a perilous state before the asteroid impact.

    The timing of these eruptions, called the Deccan Traps, has remained uncertain, however. And scientists such as Princeton University’s Gerta Keller have acrimoniously debated [Science] how much of a role they played in wiping out 60% of all the animal and plant species on Earth, including most of the dinosaurs.

    That debate won’t end today. But two studies published in Science have provided the most precise dates for the eruptions so far—and the best evidence yet that the Deccan Traps may have played some role in the dinosaurs’ demise.

    There’s long been evidence that Earth’s climate was changing before the asteroid hit. Some 400,000 years before the impact, the planet gradually warmed by some 5°C, only to plunge in temperature right before the mass extinction. Some thought the Deccan Traps could be responsible for this warming, suggesting 80% of the lava had erupted before the impact.

    But the new studies counter that old view. In one, Courtney Sprain, a geochronologist at the University of Liverpool in the United Kingdom, and colleagues took three trips to India’s Western Ghats, home of some of the thickest lava deposits from the Deccan Traps. They sampled various basaltic rocks formed by the cooled lava. The technique they used, called argon-argon dating, dates the basalt’s formation, giving a direct sense of the eruptions’ timing.

    The researchers’ dates suggest the eruptions began 400,000 years before the impact, and kicked into high gear afterward, releasing 75% of their total volume [Science]in the 600,000 years after the asteroid strike. If the Deccan Traps had kicked off global warming, their carbon dioxide (CO2) emissions had to come before the lava flows really got going—which, Sprain adds, is plausible, given how much CO2 scientists see leaking from modern volcanoes, even when they’re not erupting.

    The dates, and the increase in lava volume after the impact, also line up with a previous suggestion by Sprain’s team, including her former adviser, Paul Renne, a geochronologist at the University of California, Berkeley, that the two events are directly related: The impact might have struck the planet so hard that it sent the Deccan Traps into eruptive high gear [Science].

    The second study used a different method to date the eruptions. A team including Keller and led by Blair Schoene, a geochronologist at Princeton, looked at zircon crystals [Science] trapped between layers of basalt. These zircons can be precisely dated using the decay of uranium to lead, providing time stamps for the layers bracketing the eruptions. The zircons are also rare: It was a full-time job, lasting several years, to sift them out from the rocks at the 140 sites they sampled.

    The dates recovered from the crystals suggest that the Deccan Traps erupted in four intense pulses [Science] rather than continuously, as Sprain suggests. One pulse occurred right before the asteroid strike. That suggests the impact did not trigger the eruptions, he says. Instead, it’s possible this big volcanic pulse before the asteroid impact did play a role in the extinction, Schoene says. “It’s very tempting to say.” But, he adds, there’s never been a clear idea of how exactly these eruptions could directly cause such extinctions.

    Though the two studies differ, they largely agree on the overall timing of the Deccan eruptions, Schoene says. “If you plot the data sets over each other, there’s almost perfect agreement.”

    This match represents a victory, says Noah McLean, a geochemist at the University of Kansas in Lawrence, who was not involved in either study. For decades, dates produced with these geochronological techniques couldn’t line up. But improved techniques and calibration, McLean says, “helped us go from million-year uncertainties to tight chronologies.”

    Solving the mystery of how the dinosaurs died isn’t just an academic problem. Understanding how the eruptions’ injection of CO2 into the atmosphere changed the planet is vital not only for our curiosity about the dinosaurs’ end, but also as an analog for today, Sprain says. “This is the most recent mass extinction we have,” Sprain says. Teasing apart the roles of the impact and the Deccan Traps, she says, can potentially help us understand where we’re heading.

    See the full article here .


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