A massive volcanic eruption in what is now India about 250,000 years before the cataclysmic Chicxulub asteroid impact may have played a role in the extinction of dinosaurs, say scientists who have dated rocks from the Deccan Traps, east of Mumbai.
In December 2013, a team of scientists headed by Dr Brian Gertsch from the University of Lausanne made an expedition to the Deccan Traps – a region that preserves remnants of one of the largest volcanic eruptions on our planet.
For two weeks, they looked for volcanic rocks that might contain zircon – a uranium-containing mineral that forms in magma shortly after an eruption, and that can be used as a very precise clock for determining the age of rocks; the mineral typically crystallizes in magma containing high amounts of silica and zirconium.
The scientists collected more than 50 samples of rocks from the region representing the largest pulse of volcanism.
Fortunately, samples from both the bottom and top of this volcanic layer contained zircon, allowing the team to pinpoint the timing of the beginning and end of the Deccan Traps eruptions.
Their results, published in the journal Science, show that the eruption began 250,000 years before the Chicxulub asteroid strike (66 million years ago) and continued for 500,000 years after the impact, spewing a total of 1.5 million square km of lava.
“We have 750,000 years as the duration for the main pulse of volcanism, but it’d be nice to know whether that time represents a constant flux of magma, or if pulses of magmatism were erupted over an even shorter period of time,” said study co-author Michael Eddy, who is a graduate student at Massachusetts Institute of Technology.
The volcanism may have released dangerous levels of volatile chemicals into the air, poisoning the atmosphere and oceans.
“If models of volatile release are correct, we’re talking about something similar to what’s happening today: lots of carbon dioxide being emitted into the atmosphere very rapidly,” Mr Eddy explained.
“Ultimately what that can do is lead to ocean acidification, killing a significant portion of plankton – the base of the food chain. If you wipe them out, then you’d have catastrophic effects.”
Based on the precise dates for the Deccan Traps, the scientists believe the massive eruptions may have played a significant role in extinguishing the dinosaurs – although the exact kill mechanism may never be known.
“I don’t think the debate will ever go away. The asteroid impact may have caused the extinction. But perhaps its effect was enhanced because things were softened up a bit by the eruption of these volcanoes,” said co-author Prof Sam Bowring of Massachusetts Institute of Technology.
“The story that is emerging is that perhaps both might have been involved. Perhaps the end of the dinosaurs was caused by a one-two punch,” he said.
Blair Schoene et al. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science, published online December 11, 2014; doi: 10.1126/science.aaa0118
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