LAVA LAYERS Floods of lava formed the layers of rock in India’s Deccan Traps. Scientists sampled these layers (from location marked with a box on the map) and found that an increase in Deccan volcanism occurred within 50,000 years of the Chicxulub asteroid impact and the extinction of the dinosaurs.
Mark Richards/UC Berkeley (photo); Paul Renne/Berkeley Geochronology Center (map)
The demise of the dinosaurs may have been the result of a coordinated one-two punch.
Eruption activity in a volcanic region in present-day India appears to have increased around the time of the asteroid impact that preceded the Cretaceous extinction, scientists report in the Oct. 2 Science. The close timing between the two events leads the scientists to suggest that the impact could have triggered this volcanic shift.
Scientists have debated whether volcanic eruptions assisted the Chicxulub asteroid impact in wiping out over half of the planet’s species at the end of the Cretaceous period, roughly 66 million years ago. Previous studies showed that while eruptions in western India’s Deccan Traps began millions of years before the impact, volcanic activity surged closer to the time of the asteroid collision. In the new study, researchers report that during this volcanic shift, the amount of lava flooding the Deccan Traps roughly doubled, despite fewer overall eruptions. Scientists previously estimated that the impact and the lava surge were separated by under 100,000 years; the new study places the two events within around 50,000 years of each other.
“They both happened at effectively the same time, which is why we think there’s a causal link between them,” says study coauthor Paul Renne, a geochronologist at the Berkeley Geochronology Center in California. Earthquakes can be linked to small volcanic eruptions, so the Chicxulub impact — which would have caused the equivalent of a quake with magnitude 10 or greater — could have shifted Deccan volcanism, Renne says.
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The scientists’ analysis combined previous data with new samples taken from layers of rock in the Deccan Traps. The team analyzed the age of their samples by measuring the ratio of two forms of argon gas, a number that represents the radioactive decay of potassium to argon over time. It’s not the most precise method of dating rocks, but it allows scientists to test a wide range of samples. Renne hopes further research will narrow down the time window of when the shift in eruptions occurred, perhaps even to 5,000 years. “These results are really suggestive … we’d like them to be conclusive,” he says.
There isn’t clear evidence yet that the asteroid impact caused the surge of eruptions, says paleontologist Gerta Keller of Princeton University. This study includes samples from before and after the extinction event, but is missing samples from a period of time in between, including from the time of the extinction, says geochronologist Blair Schoene of Princeton. It will be important to fill in this gap with additional samples and data. “The end goal is to have a precise timeline for the eruptions through the entire volcanic event, and then also a precise timeline for the extinction events and the [asteroid] impact as well,” Schoene says. The new study doesn’t clarify the cause and process of the mass extinction, Schoene says. “This is certainly a great step in that direction, but there’s more work to be done.”
Understanding the process behind the extinction may prove challenging. Data show a clear link between the asteroid impact and extinction patterns worldwide, but scientists haven’t found signs of a global effect of volcanism at the end of the Cretaceous period, says paleontologist David Fastovsky of the University of Rhode Island in Kingston. And ultimately, it’s impossible to determine if volcanoes or the asteroid impact caused the extinction, he says. “The pattern that would be left from the volcanism is in fact indistinguishable from the pattern that’s left from the asteroid,” he says. “It’s fundamentally untestable.”
