Did volcanic eruptions help kill dinosaurs? | Science

By Paul VoosenFebruary 21, 2019, 2 pm

What killed the dinosaurs? The answer seems relatively simple since the discovery, a few decades ago, of a large crater impact in the Gulf of Mexico. There were 66 million years ago, an asteroid hit hard, causing massive tsunamis and erasing the sun from ashes, causing a drop in temperatures.

But the asteroid was not the only disaster to overthrow the planet at that time. Inside India today, innumerable volcanic veins open into the ground, releasing a wave of lava resembling last year's eruptions in Hawaii – except in one area of ​​the country. Texas size. Over the course of a million years, greenhouse gases from these eruptions could have increased global temperatures and poisoned the oceans, leaving life in a perilous state before the impact of climate change. # 39; asteroid.

The timing of these eruptions, known as Deccan traps, remains uncertain. And scientists such as Gerta Keller of Princeton University have debate acrimoniously what role did they play in the destruction of 60% of all animal and plant species on the planet, including most dinosaurs.

This debate will not end today. But two studies published in Science so far the most accurate dates for eruptions – and the best evidence so far that Deccan traps may have played a role in the disappearance of dinosaurs.

There was long evidence that the Earth's climate was changing before the asteroid was hit. Some 400,000 years before the impact, the planet warmed gradually by 5 ° C, to plunge into the temperature just before mass extinction. Some thought the Deccan traps could be responsible for this warming, suggesting that 80% of the lava had burst before the impact.

But new studies contradict this old vision. One of them, Courtney Sprain, geochronologist at the University of Liverpool in the UK, and his colleagues made three trips to the Western Ghats of India, where some of the thickest lava deposits in the pits are of the Deccan. They sampled various basaltic rocks formed by the cooled lava. The technique used, called argon-argon dating, dates from the formation of basalt, which gives a direct idea of ​​the moment of eruptions.

The dates of the researchers suggest that the eruptions started 400,000 years before the impact and then accelerated, releasing 75% of their total volume in the 600,000 years after the asteroid strike. If the Deccan traps had triggered global warming, their carbon dioxide (CO₂the emissions had to come in before the lava flows actually started – which, says Sprain, is plausible given the amount of CO₂ Scientists are seeing leaks of modern volcanoes, even when they are not erupting.

The dates and the increase in lava volume after the impact also correspond to an earlier suggestion from the Sprain team, especially from his former adviser, Paul Renne, geochronologist at the University of California to Berkeley, according to which the two events are directly related: The impact might have hit the planet so much that the Deccan's traps have moved up a gear.

The second study used a different method to date the eruptions. A team comprising Keller and led by Princeton geochronologist Blair Schoene examined the zircon crystals trapped between basalt layers. These zircons can be accurately dated using the decay of uranium into lead, thus providing a timestamp of the layers framing the eruptions. Zircons are also rare: it was a full-time job, which lasted several years, to sift rocks from the 140 sites they sampled.

The dates retrieved from the crystals suggest that the deccan traps burst into four intense pulses rather than continuously, as Sprain suggests. An impulse occurred just before the asteroid strike. This suggests that the impact did not trigger the eruptions, he said. Instead, it's possible that this big volcanic impulse before the impact of the asteroid has played a role in extinction, says Schoene. "It's very tempting to say it." But, he adds, it has never been clearly established that these eruptions could directly cause such extinctions.

Although the two studies differ, they largely agree on the general timing of the Deccan eruptions, says Schoene. "If you draw the data sets on top of each other, you get almost perfect agreement."

This match represents a win, said Noah McLean, a geochemist at the University of Kansas at Lawrence, who has not participated in any of these studies. For decades, dates produced with these geochronological techniques could not line up. McLean adds, "Through improved techniques and calibration, we have managed to move from uncertainties of a million years to a tight timeline.

Solving the mystery of dinosaur death is not just an academic problem. Understand how CO injection by blowouts₂ In the transformed atmosphere, the planet is vital not only for our curiosity about the end of the dinosaurs, but also as an analogue for today, says Sprain. "This is our last mass extinction," says Sprain. Teasing aside the roles of impact and Deccan traps, she says, can potentially help us understand where we are going.