What killed the dinosaurs and other life on Earth? Mega volcanoes and mass extinctions — ScienceDaily

Determining what killed off the dinosaurs 66 million years ago at the end of the Cretaceous Period has long been a topic of debate, as scientists set out to determine what caused the five mass extinction events that reshaped life on planet Earth in a geological instant. Some scientists argue that comets or asteroids that crashed into Earth were the most likely agents of mass destruction, while others argue that large volcanic eruptions were the cause. A new study led by Dartmouth published in Proceedings of the National Academy of Sciences (PNAS) reports that volcanic activity appears to have been the main driver of the mass extinctions.

The findings provide the most compelling quantitative evidence yet that the link between large volcanic eruptions and wholesale species turnover is not simply a matter of chance.

Four of the five mass extinctions coincided with a type of volcanic eruption called flood basalt, researchers say. These eruptions flood vast areas – even an entire continent – with lava in the blink of a geologic eye, just a million years. They leave behind giant fingerprints as evidence — vast, stair-like regions of igneous rock (hardened by erupted lava) that geologists call “great igneous provinces.”

To count as “large,” a large magmatic province must contain at least 100,000 cubic kilometers of magma. For context, the 1980 eruption of Mount St. Helena involved less than a cubic kilometer of magma. The researchers say that most of the volcanoes represented in the study erupted on the order of a million times more lava than that.

The team drew from three well-established datasets on geological time scales, paleobiology, and large magmatic provinces to examine the temporal relationship between the mass extinction and large magmatic provinces.

“Large areas of stair-like igneous rock from these large volcanic eruptions appear to line up in time with mass extinctions and other important climatic and environmental events,” says lead author Theodore Green ’21, who conducted the research as part of Senior. scholarship program at Dartmouth and is now a graduate student at Princeton.

In fact, a series of eruptions in present-day Siberia caused the most devastating mass extinction about 252 million years ago, releasing a giant pulse of carbon dioxide into the atmosphere and nearly drowning out all life. Witness the Siberian Traps, a vast region of volcanic rock roughly the size of Australia.

Volcanic eruptions also rocked the Indian subcontinent around the time of the great dinosaur’s death, creating what is now known as the Deccan Plateau. This, like the asteroid impact, would have had far-reaching global effects, blanketing the atmosphere with dust and toxic fumes, suffocating dinosaurs and other life, in addition to long-term climate change.

On the other hand, the researchers say, theories in favor of annihilation by asteroid impact hinge on the Chicxulub impactor, a space rock that slammed into Mexico’s Yucatan Peninsula around the same time the dinosaurs went extinct.

“All the other theories that tried to explain what killed the dinosaurs, including volcanism, were blown away when the Chicxulub impact crater was discovered,” says co-author Brenhin Keller, an assistant professor of earth sciences at Dartmouth. But there is very little evidence of similar impact events coinciding with other mass extinctions, despite decades of exploration, he points out.

At Dartmouth, Green tried to find a way to quantify the apparent connection between outbreaks and disappearances and test whether the coincidence was just coincidence or whether there was evidence of a causal connection between the two. Working with Keller and co-author Paul Renne, professor in residence of earth and planetary science at the University of California, Berkeley and director of the Berkeley Geochronology Center, Green recruited the supercomputers at the Dartmouth Discovery Cluster to crunch the numbers.

The researchers compared the best available estimates of flood basalt eruptions to periods of drastic species extinction over geological time scales, including but not limited to the five mass extinctions. To prove that the timing was more than random chance, they examined whether the explosions would match as well a randomly generated pattern and repeated the exercise with 100 million such patterns. They found that the agreement with the extinction periods was much greater than random chance.

“While it is difficult to determine whether a particular volcanic eruption caused a particular mass extinction, our results make it difficult to ignore the role of volcanism in the extinction,” says Keller. If a causal link were found between volcanic flood basalts and mass extinctions, scientists would expect that larger eruptions would bring more severe extinctions, but no such correlation has been observed.

Instead of considering the absolute size of eruptions, the research team ordered volcanic events by the rate at which they spewed lava. They found that volcanic events with the highest eruption rates did indeed cause the most destruction, producing more severe extinctions up to mass extinctions.

“Our results show that there would in all likelihood have been a mass extinction at the Tertiary Cretaceous boundary of significant magnitude, whether or not there was an impact that can now be more quantitatively demonstrated,” says Renne. “The fact that there was an impact definitely made things worse.”

The researchers also gave the numbers for asteroids. The coincidence of impacts with species turnover periods was significantly weaker and worsened dramatically when the Chicxulub impact was not taken into account, suggesting that the other smaller known impactors did not cause significant extinctions.

The scale of the Deccan Traps explosion in India suggests the stage was set for a widespread extinction even without the asteroid, Green says. The impact was the double whammy that sounded as loud as the death knell for the dinosaurs, he adds.

Flood basalt eruptions are not common in the geologic record, Green says. The last of a comparable but significantly smaller scale occurred about 16 million years ago in the Pacific Northwest.

“While the total amount of carbon dioxide being released into the atmosphere in modern climate change is still far less than the amount emitted by a large magmatic province, thankfully,” says Keller, “we are emitting it very quickly, which is reason. to be concerned”. Green says the carbon dioxide emissions are uncannily similar to the scale of the environmental impact of the flood basalts they studied. This puts climate change in the context of historical periods of catastrophe. environmental, he says.

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