About 66 million years ago, a huge asteroid slammed into our planet, unleashing a terrible firestorm that obliterated the sun and killed the dinosaurs.
Or is it? A new study has cast doubt on the theory that the dinosaurs were wiped out by a alone mountain-sized asteroid – Point your finger at volcanoes instead.
Researchers believe giant, continent-spanning “tidal basalt” eruptions caused the mass extinction — and others in Earth’s history.
The presence of an asteroid only made matters worse, they said.
Their study, published in the Proceedings of the National Academy of Sciences (PNAS) claims that volcanic activity appears to have been the primary cause of the mass extinction.
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In fact, a certain type of volcanic activity could also explain other mass extinctions in history, the researchers said.
Co-author Brenhin Keller, assistant professor of geosciences at Dartmouth College in New Hampshire, said: “All other theories that tried to explain what killed the dinosaurs, including volcanism, were overwhelmed when the Chicxulub impact crater was discovered.”
But, he added, despite decades of exploration, there is very little evidence of similar impact events coinciding with the other mass extinctions.
Keller said, “While it is difficult to determine whether a specific volcanic eruption caused a specific mass extinction event, our findings make it difficult to ignore the role of volcanism in the extinction event.”
The researchers found that four out of five mass extinctions occurred simultaneously with a type of volcanic eruption called flood basalt.
These eruptions inundated vast areas – even an entire continent – with lava in just a million years, the blink of a geological eye.
They left huge fingerprints as evidence – vast regions of step-like igneous rock (solidified by the erupted lava) that geologists call “great igneous provinces.”
To be considered “large,” a magmatic province must contain at least 100,000 cubic kilometers of magma.
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For context, the 1980 Mount St. Helens eruption involved less than a cubic kilometer of magma.
A series of eruptions in present-day Siberia triggered the most devastating mass extinction about 252 million years ago, releasing a gigantic burst of carbon dioxide into the atmosphere and suffocating almost all life.
Witnessed by the Siberian Traps, a large region of volcanic rock roughly the size of Australia.
Volcanic eruptions also rocked the Indian subcontinent around the time of the great dinosaur extinction, creating what is now known as the Deccan Plateau. Similar to the asteroid impact, this would have had far-reaching global effects, blanketing the atmosphere with dust and noxious fumes, choking out dinosaurs and other life, and altering the climate for long periods of time.
Researchers compared the best available estimates of flood basalt eruptions to periods of drastic species extinctions on the geologic timescale, including but not limited to the five mass extinctions.
Paul Renne, Professor-in-Residence of Earth and Planetary Sciences at the University of California, Berkeley, said: “Our results indicate that there would have been, in all likelihood, a large-scale Cretaceous-Tertiary extinction event that regardless of whether there was an impact or not, which can now be shown more quantitatively.
“The fact that there was an impact undoubtedly made matters worse.”
The outbreak rate of Deccan Traps in India suggests the conditions for a widespread extinction were set even without the asteroid, said lead author Theodore Green.
Green, who conducted this 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 loudly rang the death knell for the dinosaurs.
Flood basalt outbursts are not common in the geologic record, Green said. The last of comparable but much smaller scale occurred about 16 million years ago in the US Pacific Northwest.
“While the total amount of carbon dioxide released into the atmosphere in modern climate change is still very much less than the amount emitted by a large volcanic province, luckily we are emitting very rapidly,” Keller said, “which is why be concerned.”
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