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Boffins: We know what KILLED the DINOS – and it wasn't just an asteroid

The truth at long last?

For decades, scientists have been arguing over what killed the dinosaurs 66 million years ago – an asteroid or geological activity. Now it turns out both sides may be right.

In 1981, scientist Luis Walter Alvarez proposed that a massive asteroid slammed into the Earth, causing large-scale damage and clouds of toxic chemicals that snuffed out the dominant dinosaurs. He backed this up with the discovery of a massive impact crater at Chicxulub off the Mexican coast, marked in geology by the K-T boundary between the Cretaceous and Tertiary periods.

The theory quickly gained support, but there was still a large body of opinion that the smoking gun wasn't the asteroid per se, but an area of volcanoes in what's now India called the Deccan Traps. The feature spewed out enormous amounts of lava that covered half of the subcontinent and could have severely altered the world's climate.

But a team from University of California Berkeley has published a paper in Science which suggests that both events would have contributed to the dinosaurs' demise. The asteroid's impact would have been a massive shock to Earth's ecosystem, but turned the Deccan Traps from a slow eruption into something much, much worse.

The Berkeley scientists took samples from the Deccan Traps that cover 500,000 years on either side of the time of the asteroid's impact. Using argon-40/argon-39 isotope dating, they established the rate of flow of the volcanos over that time.

"At the KT boundary, we see major changes in the volcanic system of the Deccan Traps, in terms of the rate at which eruptions were happening, the size of the eruptions, the volume of the eruptions, and some aspects of the chemistry of the eruptions, which speaks to the actual processes by which the magmas were generated," said Paul Renne, director of the Berkeley Geochronology Center.

"All these things changed in a fundamental way, and increasingly it seems they happened right at the KT boundary. Our data don't conclusively prove that the impact caused these changes, but the connection looks increasingly clear."

The asteroid that hit Earth was massive, at least six miles in diameter, and the impact would have shaken the crust violently. The resultant dust cloud coated the surface of the entire planet and led to mass animal die-offs, both on land and in the oceans.

"The biodiversity and chemical signature of the ocean took about half a million years to really recover after the KT boundary, which is about how long the accelerated volcanism lasted," Renne said. "We are proposing that the volcanism unleashed and accelerated right at the KT boundary suppressed the recovery until the volcanoes waned."

It's not a certainty that the impact triggered the Deccan Traps to spew out more material – the team acknowledges that a force eight or nine earthquake might have had the same effect. But the chronological closeness of the two events suggests a link.

"If our high-precision dates continue to pin these three events – the impact, the extinction, and the major pulse of volcanism – closer and closer together, people are going to have to accept the likelihood of a connection among them," said Mark Richards, a UC Berkeley professor of earth and planetary science.

"The scenario we are suggesting – that the impact triggered the volcanism – does in fact reconcile what had previously appeared to be an unimaginable coincidence." ®

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