Science has debated for a very long time what killed the dinosaurs 66 million years ago. Several studies have focused on the causes of the five significant extinction events that changed life on Earth in a geological instant.
According to some scholars, asteroids or comets colliding with Earth were the most obvious culprit and the most plausible sources of massive catastrophes and the mass extinction of dinosaurs. Other scientists contend that enormous volcanic explosions mainly caused the extinction events.
A new study from Dartmouth published on September 12 in the Proceedings of the National Academy of Sciences (PNAS) showed that volcanic activity is thought to have been the primary cause of mass extinctions.
Dartmouth’s new findings give the most persuasive quantitative evidence to date that the link between massive volcanic eruptions and widespread species turnover is not a coincidence.
The researchers claim that four of the five global extinctions occurred concurrently with a volcanic eruption known as “flood basalt.” These eruptions cover enormous areas—even an entire continent- in less than a million years—with lava. They leave behind massive fingerprints as proof, so-called “large igneous provinces,” which are vast areas of step-like igneous rock that have crystallized after lava eruptions.
How ‘large’ is large?
To be considered “big,” an igneous province must contain at least 100,000 cubic kilometers of magma. A cubic kilometer (0.24 cubic mile) has a volume equal to 264 billion gallons or 400,000 Olympic swimming pools. For comparison, the 1980 Mount St. Helens eruption discharged less than one cubic kilometer of magma.
According to the researchers, the majority of the volcanoes included in the study erupted on the order of a million times more lava than that.
The research team drew on three well-known datasets on a geologic time scale, paleobiology, and large igneous provinces, to investigate the temporal relationship between mass extinction and large igneous provinces.
Theodore Green, who conducted this research as part of the Senior Fellowship program at Dartmouth, is the study’s lead author. He claims that “major extinctions and other significant climatic and environmental events tend to line up in time with these enormous step-like sections of igneous rock from these big volcanic eruptions.”
The most severe mass extinctions occurred around 252 million years ago due to a series of eruptions in modern-day Siberia that blasted a massive pulse of carbon dioxide into the atmosphere and nearly suffocated all life. The Siberian Traps, a vast area of volcanic rock almost the size of Australia, serve as a witness.
Around the time of the massive dinosaur extinction, the Indian subcontinent was also shaken by volcanic eruptions, which helped to create the Deccan plateau. This would have had similar worldwide repercussions as the asteroid strike, covering the atmosphere in dust and toxic fumes, choking dinosaurs and other species, and long-term climate change.
The Chicxulub impactor, a space rock that impacted Mexico’s Yucatan Peninsula about the same time the dinosaurs went extinct, is essential to the theories supporting annihilation by an asteroid impact, according to the researchers.
The discovery of the Chicxulub impact crater, according to co-author Brenhin Keller, an assistant professor of earth sciences at Dartmouth, “steamrolled all other theories that attempted to explain what killed the dinosaurs, including volcanism.” Despite years of research, he notes that there is very little proof of impact events comparable to those that caused the earlier great extinctions.
Was the correlation between eruptions and extinctions simply a coincidence?
To determine whether the correlation between eruptions and extinctions was simply a coincidence or if there was proof of a causative connection between the two, Green set out to quantify the connection in Dartmouth. He used the Dartmouth Discovery Cluster’s supercomputers to crunch the statistics while working with Keller and co-author Paul Renne, professor emeritus of Earth and planetary science at the University of California, Berkeley, and director of the Berkeley Geochronology Center.
The researchers analyzed the five mass extinctions and other eras of extreme species extinction in the geological timescale with the best estimates of flood basalt eruptions. They tested whether the explosions would line up just as well with a randomly generated pattern and did the experiment 100 million times to show that the timing was more than just chance. They found a much greater degree of concordance with extinction timeframes than they had anticipated.
Despite the fact that it can be challenging to determine whether a given volcanic eruption served as the catalyst for a certain mass extinction, Keller asserts that “our findings make it difficult to overlook the importance of volcanism in extinction.”
Scientists anticipate that more intense eruptions would result in more severe extinctions if a causal relationship between volcanic flood basalts and mass extinctions could be established. This connection, however, has not been discovered.
The research team ranked the volcanic episodes according to how quickly lava spewed out instead of considering the eruptions’ exact magnitude. They discovered that the most destructive volcanic events resulted in more severe extinctions, all the way to mass extinctions.
“It is now quantitatively proved that a mass extinction of some significance would have most likely occurred at the Cretaceous Tertiary boundary, whether or not there was an impact,” claims Renne.
The researchers also performed calculations for asteroids
When the Chicxulub impactor was not considered, the correlation of impacts with times of species turnover was noticeably weaker and severely worsened. This shows that other smaller known impactors did not significantly contribute to extinction rates. According to Green, flood basalt eruptions are uncommon in the geologic record. A similar but much smaller-scale event occurred about 16 million years ago in the Pacific Northwest.
Keller notes that although the total amount of carbon dioxide being released into the atmosphere as a result of modern climate change is still, happily, considerably less than the amount released by a significant igneous province, “we’re emitting it very fast, which is cause for concern.” Green claims that the rate of the environmentally damaging flood basalts they researched is uncomfortably similar to the current carbon dioxide emissions. According to him, this situates climate change within the context of earlier times of environmental calamity.
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