Chicxulub or Deccan volcanism? That’s one of the questions being bandied around at this year’s American Geophysical Union conference here in San Francisco.
This year, Deccan volcanism is gaining, after years of Chicxulub being ahead.
Either or both theory could be the answer to a big question: what killed the dinosaurs?
Some disaster, known as the KT or Cretaceous–Tertiary extinction event, destroyed about 75% of all species on Earth 65 million years ago. Since the 1980s, the money’s been on a giant meteor that hit Mexico’s Yucatan peninsula about that time. Scientists know about the meteor because of the hole it left behind, known as the Chicxulub crater.
But a different hypothesis is gaining ground. First proposed in 2004 by Gerta Keller, a professor of geology and paleontology at the Geosciences Dept. at Princeton University, it suggests that climate changes were caused by a vast barrage of volcanoes erupting on southern India's Deccan plateau were to blame for the dinosaurs' demise.
This wasn’t your basic volcano eruption. Think, instead, of thousands of volcanoes spewing lava 11,500 feet (3,500 meters) thick in places, pouring across the length of the Indian subcontinent, in at least 30 volcanic “pulses” over the course of about 10,000 years.
While the Chicxulub impact released between 50 to 150 gigatons (one billion tons) of sulfur dioxide, the Deccan eruptions released 10,000 gigatons, says Vincent Courtillot, director of the Institut de Physique de Globe de Paris University.
“They were fire fountains in excess of one mile high over 250 miles (400 kilometers.) They threw their gases into the stratosphere. The event was almost immediately global,” says Courtillot.
New data is being presented at the meeting to support the hypothesis. For example, recent research has shown that instead of lasting a million years, as had been thought, the eruptions actually went on for “less than 10,000 years, says Courtillot.
While the ocean can absorb and equalize the output of one volcano over a few thousand years, these megaflows happened so quickly that the ocean couldn’t keep up, Courtillot says, “producing a mass extinction.”
Keller also presented new data from eight rock core samples taken by Indian petroleum engineers, showing that after each megaflow, fewer and fewer fossils were found.
“Once the first flow hits the area, species disappear,” she says.
By Elizabeth Weise
Photo: A high resolution topographic map of the Yucatan Peninsula. In the upper left portion of the peninsula, a faint arc of dark green is visible indicating the remnants of the Chicxulub impact crater. (NASA/Getty Images)
