Asteroid impact, volcanoes together wiped out dinosaurs

Washington

An asteroid impact 66 million years ago accelerated the eruptions of volcanoes in India for hundreds of thousands of years, dealing a one-two punch that may have wiped out the dinosaurs, a new study has found.

The new data shows that the Deccan Traps lava flows in western India, which at the time were erupting at a slower pace, doubled in output within 50,000 years of the asteroid or comet impact that is thought to have initiated the extinction of many land and marine animals, including the dinosaurs.

Both the impact and the volcanism would have blanketed the planet with dust and noxious fumes, drastically changing the climate and sending many species to an early grave.

The researchers collected lava samples from the Deccan Traps east of Mumbai, sampling flows from near the beginning, several hundred thousand years before the extinction and near the end, some half a million years after the extinction.

High-precision argon-40/argon-39 isotope dating allowed them to establish the chronology of the flows and the rate of flow over time.

"Based on our dating of the lavas, we can be pretty certain that the volcanism and the impact occurred within 50,000 years of the extinction, so it becomes somewhat artificial to distinguish between them as killing mechanisms — both phenomena were clearly at work at the same time," said lead researcher Paul Renne, a professor at the University of California Berkeley.

The geologists argue that the impact abruptly changed the volcanoes' plumbing system, which produced major changes in the chemistry and frequency of the eruptions.

After this change, long-term volcanic eruptions likely delayed recovery of life for 500,000 years after the KT boundary, the point in between the Cretaceous and Tertiary periods.

"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 co-author Mark Richards, professor at UC Berkeley.

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

Scientists have argued about whether the impact was the cause of the mass extinction that occurred at the same time, the end of the Cretaceous period, or the KT boundary.

Some argued that the huge volcanic eruptions in India known as the Deccan Traps, which occurred around the same time, were the main culprit in the extinctions.

Others insisted the death knell had been the impact, which left behind a large crater dubbed Chicxulub off Mexico's Yucatan peninsula, and viewed the Deccan Traps eruptions as a minor sideshow.

The study was published in the journal Science. — PTI