Contrarian theory argues against meteorite killing dinosaurs.
A worldwide burp of volcanic gases caused the mass extinction that wiped out dinosaurs and other creatures 65 million years ago, says research reported this week. It?s the latest argument from a group that has been trying for some time to discredit the leading theory ? that a meteorite striking Mexico led to the mass die-offs.
The international team says that we should instead blame plumes of climate-altering gas given off by monumental lava flows that stretch hundreds of kilometres across India.
The Deccan Traps, as they?re called, have been suspected before of having some sort of global impact around the end of the Cretaceous period and the beginning of the Tertiary, known as the K?T boundary. Earlier research had dated the main outburst of the lava flows as occurring within 800,000 years of the boundary. But the new analysis uses tiny plankton fossils, trapped between lava layers, to date the flow to the boundary itself.
?This is the first time we can link the main phase of the Deccan Traps to the mass extinction,? says team leader Gerta Keller, a palaeontologist at Princeton University in New Jersey. Keller and Thierry Adatte of the University of Neuch£tel in Switzerland presented their research on 30 October in Denver, Colorado, at the annual meeting of the Geological Society of America.
Earlier work indicated that Deccan-like eruptions would have resulted in huge amounts of sulphur dioxide quickly building up in the atmosphere. And new work in press, from Vincent Courtillot of the Institut de Physique du Globe in Paris and his colleagues, suggests that the Deccan flows released some 50?100 gigatonnes of sulphur dioxide and carbon dioxide ? about 10 times more than estimated from the meteorite strike, at Chicxulub on Mexico?s Yucat£n Peninsula.
But scientists who have worked on the impact theory were quick to question the new analysis. The amount of gas spewed out by the Deccan flows would have been insufficient to cause the extinctions, says Philippe Claeys of the Free University in Brussels, Belgium. ?It is not possible,? he says.
Jan Smit, of the Free University in Amsterdam, adds that he thinks that when the meteorite hit, it would have put out more gas in vaporizing rock than the entire Deccan flow. ?I don?t believe they have said anything new here,? he says.
Keller has long challenged the Chicxulub theory. Several years ago, her team reported that analysis of a core drilled into the Chixculub crater suggested that the impact dated to 300,000 years earlier than the K-T boundary. Later work, from a core drilled along the Brazos River in Texas, also seemed to support this notion of a 300,000-year gap.
But the work is not clear-cut. Another report presented at the Denver meeting this week suggested that the sediments in the Brazos core had been reworked by geological forces over time, thus confusing the dating of what happened when.
In their Indian studies, the team focused on an area around Rajahmundry, on the Bay of Bengal. In the Krishna-Godavari basin there, they examined four quarry outcrops that have lava layers below them and that sit on top of a 9-metre-thick layer of marine sediments.
"The key to our success was finding marine sediments with microfossils," says Keller. Within those, she reported finding tiny fossils of ocean creatures, known as foraminifera, that exploded in a massive bloom after the mass extinction.
Minerals in the sediments also suggested that the climate was more humid after the gas eruption, Adatte says. "This shows how significant the lava flows were," he says.
Next year, the team hopes to drill a new core at Rajahmundry to date the sediments more precisely, and to understand exactly how the gases affected the growth of plankton.
An Indian oil company also has cores taken from the area, which Keller hopes to examine.
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Dalton, R. Gas may be to blame for extinction. Nature (2007). https://doi.org/10.1038/news.2007.205