San Francisco: The age of the dinosaurs ended abruptly about 65 million years ago when some catastrophic event drove them to extinction, and now a vehement controversy over their disappearance is emerging anew.

Like many scientific debates, this one is hot and has been going on for years, but only one side is having its say in San Francisco this week, and the dinosaurs have no one to speak for them.

Mysterious disappearance: A file photo of a model of a dinosaur at Visweswaraya Industrial and Technological Museum in Bangalore. Hemant Mishra/ Mint

The origins of the big debate began nearly 30 years ago when the geologist Walter Alvarez at Berkeley and his father, Luis, a Nobel physics laureate, proposed that a cosmic collision by an object from space at least 6miles (9.6km) wide crashed just off Mexico’s Yucatan peninsula about 65 million years ago and created what is known as the Chicxulub crater.

Leaders of the Indian volcano theory held the stage on Monday at Moscone Center West in San Francisco, where some 14,000 scientists of many disciplines are gathering this week for the annual meeting of the American Geophysical Union. They agree with the Alvarez argument about the general time frame of the mass extinction, saying it occurred about 65.7 million years ago at a crucial period in earth’s history called the Cretaceous/Tertiary boundary.

They also agree it wasn't only the dinosaurs that went extinct but the vast majority of plants and other life forms on earth died along with them. And when the mass extinction was over, the mammals of the world finally had their opportunity to thrive and evolve and dominate the earth.

But Gerta Keller of Princeton University and her colleagues part ways with the Berkeley scientists on the cause. Keller, joined by Vincent Courtillot of the University of Paris and Sunil Bajpai , of the Indian Institute of Technology, Roorkee,delivered their findings at a press conference on Monday and will present detailed scientific reports all this week.

At the press conference, Keller insisted that the impact crater was formed at least 300,000 years before the great extinction and “caused no species extinctions"—certainly not to the dinosaurs. She came to her conclusion, in part, by age-dating clusters of mineral spherules that presumably spewed out of the Chicxulub crater and landed in Texas, where Keller said she gathered and tested them.

Instead, she argued, the extinction coincided with three or four waves of volcanism in a region of north-west India known as the Deccan traps. She said both fossilized plankton and even dinosaur eggs covered with lava found in the Deccan area bore still more testimony to back her theory. The mass extinction, she said, “was complete by the fourth eruption".

Keller’s theory of Deccan volcanism as the cause of the dinosaurs’ extinction “has been vastly underestimated", she said, while “the crater's importance as evidence has been vastly overestimated".

“This impact caused no extinctions."

Walter Alvarez, who was not at this week's meeting of scientists and whose father died 10 years ago, rejected the idea that volcanism in India was the sole cause of the mass extinction.

In a phone interview and an email exchange he insisted on Monday that the arguments by Keller and her colleagues “have been examined in detail by other scientists and generally rejected".

“Few experts on the mass extinction would agree with Keller that the Chicxulub impact is older than the mass extinction," he said.

©2008/The New York Times