About 66 million years ago, a giant asteroid crashed into our planet, unleashing a terrible firestorm that blanked out the sun and killed the dinosaurs.
Or did he? A new study has cast doubt on the theory that the dinosaurs were wiped out solely by a mountain-sized asteroid – pointing the finger at volcanoes instead.
Huge eruptions of “flood basalt” spanning a continent are the cause of the mass extinction – and others in Earth’s history, researchers believe.
The presence of an asteroid only made matters worse, they said.
Their study, published in the Proceedings of the National Academy of Sciences (PNAS), says volcanic activity appears to have been the primary driver of the mass extinctions.
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In fact, a particular type of volcanic activity may also explain other mass extinctions in history, the researchers said.
Co-author Brenhin Keller, assistant professor of earth sciences at Dartmouth College in New Hampshire, said: “All other theories that tried to explain what killed the dinosaurs, including volcanism, have been crushed. when the Chicxulub impact crater was discovered.”
But, he added, there is very little evidence of similar impact events that coincided with the other mass extinctions despite decades of exploration.
Keller said, “While it is difficult to determine whether a particular volcanic explosion caused a particular mass extinction, our results make it difficult to ignore the role of volcanism in the extinction.”
Researchers have found that four out of five mass extinctions occur at the same time as a type of volcanic outpouring called flood basalt.
These eruptions have flooded large areas – even an entire continent – with lava in just a million years, in the blink of a geologic eye.
They left giant fingerprints as evidence – vast regions of staircase-like igneous rock (solidified from erupting lava) that geologists call “great igneous provinces”.
To be considered “large”, an igneous province must contain at least 100,000 cubic kilometers of magma.
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For context, the 1980 eruption of Mount St. Helens involved less than a cubic kilometer of magma.
A series of eruptions in present-day Siberia triggered the most destructive of mass extinctions around 252 million years ago, releasing a gigantic pulse of carbon dioxide into the atmosphere and snuffing out nearly 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 die-off, creating what is now known as the Deccan Plateau. This, like the asteroid strike, would have had far-reaching global effects, blanketing the atmosphere in toxic dust and fumes, suffocating dinosaurs and other life, and altering the climate for long periods of time. .
The researchers compared the best available estimates of flood basalt eruptions with periods of drastic species destruction across geologic timescales, including but not limited to all five mass extinctions.
Paul Renne, Professor-in-Residence of Earth and Planetary Sciences at the University of California, Berkeley, said: “Our results indicate that in all likelihood there was a mass extinction at the Cretaceous Tertiary boundary of a significant magnitude, regardless of whether there was an impact or not, which can be shown more quantitatively now.
“The fact that there was an impact definitely made it worse.”
The eruption rate from India’s Deccan Traps suggests the stage was set for widespread extinction even without the asteroid, said lead author Theodore Green.
Green, who conducted the research as part of the senior fellowship program at Dartmouth and is now a graduate student at Princeton, added that the impact was the double whammy that spelled the death knell for dinosaurs.
Flood basalt eruptions are not common in the geologic record, Green said. The last of a comparable but significantly smaller scale occurred about 16 million years ago in the American Pacific Northwest.
“While the total amount of carbon dioxide released into the atmosphere as part of modern climate change is still far below the amount emitted by a large igneous province, fortunately,” Keller said, “we’re emitting it very quickly. , which is the reason to be concerned.”
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