Sixty-six million years ago a cataclysmic event cause an entire population to go extinct. We know them today as the dinosaurs, but the reason for their extinction has divided the scientific community into two main camps: by asteroid or by volcanic eruption.
Joel Achenbach of the Washington Post writes on a recent paper published in Science that discusses the latest dinosaur extinction discovery that has come out of India. The new evidence comes from within the Deccan Traps, a geological formation that covers 200,000 square miles around Mumbai. The area was created by a volcanic eruption. Scientists were able to date the crystal samples from the site, which contain trace amounts of uranium that have since decayed into lead. Because it's well-known how long uranium takes to decay, scientists were able to pinpoint when the volcano began its devastating eruption 250,000 years—before the extinction event. But it ended around 500,000 years after, adding an interesting twist.
This new evidence has Blair Schoene, lead author of the paper and a Professor of Geosciences at Princeton, favoring both catastrophes as the cause for the mass extinction. His co-author, Gerta Keller, has a more one-sided view of the event, maintaining the theory that the Deccan Traps eruption caused the mass-extinction. She views that the asteroid impact happened too early to cause the die-off and sees the findings in India as strength in the case that a volcanic eruption was the extinction event.
Schoene and his co-authors nailed down the age of the Deccan Traps with a painstaking search for zircons, tiny minerals that are rarely found in basalt lavas. The researchers did find a few zircons in the lava flows, but many of their samples came from volcanic ash trapped in between the basalt, in layers called red boles. The red boles are zones of intensely weathered rock and sediment sandwiched between the lava.
Tests on the zircons show that volcanic activity began 66.288 million years ago, and 80 to 90% of the entire volume of lava flooded out within about 750,000 years, the researchers reported. The Deccan Traps generated about 123,000 cubic miles (512,000 cubic kilometers) of lava.
With new dates from only the top and bottom of the lava flows, the researchers have not yet worked out how quickly the molten rock oozed from the region's broad volcanoes and fissures. Earlier studies indicated that the lava tap turned on and off over time, with pulses of activity. Work in progress by Renne and others suggests there was a major surge soon after the Chicxulub impact. Schoene's group will return to India in January to search for more zircons, in hopes of further correlating volcanic activity with the mass extinction.