Oct 29, 2007
New evidence dug from the shores of the Bay of Bengal supports the radical idea that it was a series of monumental volcanic eruptions that wiped out the dinosaurs, not a meteor impact in the Gulf of Mexico.
The largest of the massive Deccan traps volcanic eruptions in central India sent basalt lava east across the continent and into the sea.
There, near the town of Rajahmundry, an international team of geologists has found marine fossils deposited immediately on top the largest ancient lava flow there.
The fossils, which match those found elsewhere, are believed to be species that evolved just after the Cretaceous-Tertiary (K-T) mass extinction 65.5 million years ago.
"We went to the Rajahmundry area because volcanic layers, called traps ... are found in this area interbedded in shallow marine sediments that contain microfossils, which yield age control," says geologist Professor Gerta Keller of Princeton University (http://www.princeton.edu).
Keller and her colleagues will present their new evidence later this week at the meeting of the Geological Society of America (http://www.geosociety.org/) in Denver.
There are two traps at Rajahmundry, each containing up to four individual pulses of lava, she says.
The lower trap represents 80% of the Deccan eruption. Some 9 metres higher, above the fossilised remnants of a quiet shallow sea, the upper trap marks the finale of the entire volcanic episode, which came some 280,000 years after the mass extinction event.
The discovery confirms two important things, says Keller.
First, that the most massive Deccan eruption and the K-T mass extinction happened at the same time.
Second, that the later, final eruption is timed right to have slowed the recovery of many living things. This slow recovery has long been a mystery to palaeontologists, she says.
As for how an eruption in India killed dinosaurs worldwide, she says it's all about the gases.
The Deccan traps represent one of the largest known eruptions on the surface of the earth. The event released vast amounts of greenhouse gases into the atmosphere, which would have caused very rapid climate change.
One thing that could confirm or interfere with Keller's theory would be resolving the timing of the various pulses of lava within each trap, says Professor Steve Self, a Deccan Traps volcanologist at the UK's Open University (http://www.open.ac.uk/).
"The one thing we don't know is the time between the eruptions," Self says.
If there was enough time for the atmospheric system to recover between pulses, then the overall effect of the eruption would have been greatly diminished, he says.
Another big matter of speculation, which also faces those who believe a meteor impact wiped out the dinosaurs, is exactly how the earth's atmosphere responds to such events.
As nothing like the Deccan traps has happened in human history, all researchers can do is try to model the effects by scaling up smaller eruptions, like the record cold weather that followed the 1783 eruption of Laki in Iceland.