Scientists have found new evidence that the KT extinction event 66 million years ago was a combination of both an asteroid impact and subsequent increased volcanic activity. Specifically, they think the Chicxulub impact may have doubled the activity of already present volcanism at the time, ultimately leading to the extinction of more than 80% of animal species, including the dinosaurs.
Such a theory has been proposed before, but previous ideas suggested the impact triggered fresh volcanism. This latest theory suggests a period of volcanism lasting hundreds of thousands of years was intensified by the impact – and those animals that weren’t wiped out in the initial blast were ultimately wiped out by the drastically changed climate, which included periods of global warming and cooling, and acid rain. The research, led by the University of California, Berkeley, is published in the AAAS journal Science.
“The fact that volcanism and the impact [may have] happened at the same time has been known for a while,” study co-author Loÿc Vanderkluysen, from Drexel University in Philadelphia, told IFLScience. “But we found out that since the eruption started a few hundred thousand years before the impact, the idea that the whole eruption was triggered by the impact sort of lost ground when the volcanism started before.”
The scientists came to their conclusion by dating the lavas at the Deccan Traps, east of Mumbai in India, which began forming 66 million years ago. They sampled flows from before, during, and after the extinction, using high-precision argon-40/argon-39 isotope dating to study their chronology. Results suggested their output doubled within 50,000 years of the asteroid or comet impact.
Shown are the layered lava flows of the Deccan Traps, east of Mumbai, India. Mark Richards/UC Berkeley.
Such extremely large volcanic events are estimated to occur every 20 million years, but the chance of the increase in volcanism and the asteroid impact occurring at the same time, within 50,000 years, for unrelated reasons is thought to be extremely unlikely.
“The scenario we are suggesting – that the impact triggered the volcanism – does in fact reconcile what had previously appeared to be an unimaginable coincidence,” said co-author Mark Richards, from the University of California, Berkeley, in a statement.
The location of the impact and the Deccan Traps were thought to be on opposite sides of the world at the time, but such was the size of the impact event that every location on Earth would have experienced a magnitude 9 earthquake – enough to trigger the increased volcanic activity. It’s possible that volcanic activity in other locations was also intensified.
The exact relationship between the impact and the increase in volcanic activity is not fully known, though. “The mechanism is not perfectly understood,” Vanderkluysen told IFLScience. “This is going to be the area of future research for us.” He noted, though, that such events are not unprecedented; volcanic activity in Indonesia in 2006 has been linked to earthquakes in the vicinity.
As the impact and increase in activity 66 million years ago occurred so close together, it’s also difficult to tell which was the major contributor to global extinction. “We’re not sure either, separately, would have nearly the same effect,” said Vanderkluysen. “The impact certainly caused a lot of extinction, but the volcanism prevented the recovery of the ecosystem. It might have made things a lot worse for those organisms that survived for maybe a decade after the impact, and then could not find a good source of food due to a prolonged period of thousands of years of volcanism that followed.”
This will be the subject of future research, and aside from better understanding the relationship between the impact and volcanism, the scientists also want to see how organisms on land and in the oceans were affected differently by the event.
Image in text: The volcanic region is shown in red, while the researchers took samples from the area marked by the rectangle. Paul Renne, Berkeley Geochronology Center & UC Berkeley.
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