Published online 16 December 2008 | Nature | doi:10.1038/news.2008.1308

News

Volcanoes implicated in death of dinosaurs

Groups argue that an impact wasn't to blame.

Three research teams have released evidence suggesting that the dinosaurs were wiped out 65 million years ago by massive volcanic eruptions in India, rather than a meteorite impact, as most scientists have thought.

What did kill the dinosaurs?NSF

The research, based on samples from drilling in India, shows that four large eruptions coincided with the Cretaceous/Tertiary (K/T) extinction event, which killed off a large fraction of life on land and in the seas.

Multiple outbursts from the massive Deccan lava flows filled Earth's atmosphere with sulphur dioxide, snuffing out most life forms, teams from the United States, India and France said at the 15–19 December autumn meeting of the American Geophysical Union (AGU) in San Francisco, California.

One of the presenting researchers, Gerta Keller, a palaeontologist at Princeton University in New Jersey, called the evidence "the most serious challenge" to the theory that a meteorite or comet caused the extinctions. The extraterrestrial explanation, first proposed in 1980, has been supported by most geoscientists since the early 1990s, when researchers discovered the buried Chicxulub crater beneath the Yucatan Peninsula in Mexico and dated that giant scar to the time of the extinctions.

But the new evidence may reignite a longstanding debate over the role played by the Indian eruptions, which some researchers have implicated in the past. "They are definitely doing what needs to be done," says Paul Renne from the Berkeley Geochronology Center in California. "I think the focus of the cause of the extinction has come back more to the Deccan flows."

Evolving mystery

Walter Alvarez, the geologist at the University of California, Berkeley, who first linked the Chicxulub impact to the extinctions, says the AGU reports are a new phase of an evolving, complicated mystery.

"Chicxulub is so precisely coordinated in time to the extinction, it is hard to say it is not the trigger," he says. "What fascinates me is why the Deccan [eruptions] are going on at the same time. Does it play a role? Maybe it does."

The latest work is by researchers who have long questioned the extent of the Mexico meteorite's impact1,2,3, particularly Keller and Vincent Courtillot of the Institute of Global Physics in Paris. Sunil Bajpai, a palaeontologist at the Indian Institute of Technology at Roorkee, also presented evidence linking the Indian eruptions to the extinctions.

The Deccan lava flows run from Mumbai across central India. As thick as 3,500 metres, they are difficult to date because of the lava's geochemical make-up and the lack of sediments containing telltale fossils.

Getting to the core

Keller and her team examined eight cores drilled by India's Oil and Natural Gas Corporation. Because the cores were taken from areas close to the Bay of Bengal, they included marine sediments.

At the depth corresponding to the K/T boundary period, the team identified normal marine plankton fossils being eliminated by the repeated lava flows, followed by the emergence of fossils of opportunistic plankton known to bloom after mass extinctions.

ADVERTISEMENT

"The first massive eruption resulted in over 50% decline in plankton diversity," says Keller. "No recovery occurred between subsequent eruptions and the mass extinction was completed by the fourth eruption."

Courtillot's team looked at Earth's intermittent changing magnetic fields that leave a directional record in cooled volcanic rock. By analysing the magnetic direction of lava samples from 169 locations, his group produced a Deccan lava flow map.

This sampling identified 30 major eruptions extending 100–800 kilometres, he says. He calculates that the eruptions happened far faster than previously estimated; and the two largest eruptions were dated to within 1 million years of the K/T extinctions. One of these flows was estimated to produce 10 billion–150 billion tonnes of sulphur dioxide. He estimated the Yucatan meteorite strike as releasing 50 billion–500 billion tonnes of gas.

A new core is to be drilled to provide a continuous record of sediments to better date events surrounding the eruptions. 

  • References

    1. G. Keller et al, Palaeogeography Palaeoclimatology Palaeoecology, in press (2008).
    2. A.L. Chenet et al, EPSL 263, 1-15 (2007).
    3. A.L. Chenet et al, J. Geophys. Res. 113, B04101 (2008).
Commenting is now closed.