India's Smoking Gun: Dino-killing Eruptions

The Deccan Traps of India are one of Earth's largest lava flowsever, with the potential of having wreaked havoc with the climate ofthe Earth - if they erupted and released climate-changing gases quicklyenough. French and Indian geologists have now identified a 600-meter(2000-foot) thick portion of the lava that may have piled up in aslittle as 30,000 years - fast enough to have possibly caused a deadlyglobal climate shift.

"Our working hypothesis is that the majority of the totalvolume of lava might have been erupted in only a few major eventsspread over only a small fraction of millennia," said Anne-Lise Chenetof the Laboratoire de Paleomagnetisme, Institut de Physique du Globe deParis (IPGP).

To test that hypothesis, the researchers have combined alreadyknown ages of the traps gathered from radiometric dating with magneticfields frozen in the rocks. Volcanic rocks record information about theEarth's magnetic field with magnetic minerals that align with Earth'sfield like millions of tiny compasses before the lava cools. When thelava solidifies, the compasses are locked in place.

Lava layers that erupted within two or three centuries of eachother will record similar magnetic fields, explains Chenet. Longer thanthat and the natural changes in Earth's magnetic field start to showup. The team also incorporated information about the lava's chemistry,the way it flowed and piled up and the red weathered soils between lavalayers to estimate the timing and number of major volcanic pulses.

All that information points to the 600 meters (2000 feet) oflava pouring out in as little as 30,000 years. This is enough to havepossibly released a climate-altering amount of sulfur gases, saysChenet. An estimate of just how much gas is still being worked out.

Chenet is scheduled to present the latest results of theteam's work on Wednesday, 10 August, at Earth System Processes 2, ameeting co-convened by the Geological Society of America and GeologicalAssociation of Canada this week in Calgary, Alberta, Canada.

Chenet and her colleagues' new work on the Deccan Traps isjust the latest in a series of discoveries which appear to weaken thecase implicating the Chicxulub impact as the primary player in theCretaceous-Tertiary (K-T) mass extinction.

"As originally proposed by Vincent Courtillot in 1986, thevolcanism might be a key player in mass extinctions," said Chenet."Research in India has shown the remnants of the impact - iridium insediments - sandwiched between lava flows, implying that volcanismstarted before the impact."

In fact, most mass extinctions over the past 300 million yearshave coincided with large volcanic events, said Chenet. The generalrule is that massive volcanism like the Deccan Traps correlates withall major mass extinctions in Earth's history, she said.

"In only one case is there evidence for both volcanism andimpact," she said. And that is the K-T mass extinction that ended thereign of the dinosaurs. "Our view is that impact added to the stressalready generated by an ongoing massive eruption, enhancingsignificantly the extent of the extinction, which would however havetaken place even if the impact had not occurred."

Wiped out in the K-T mass extinction were 80-90% of marinespecies and about 85% of land species. All land animals larger than 25kg (55 lbs) were obliterated.

The Deccan Traps are a huge pile of basaltic lava extendingover more than 500,000 square kilometers. Its original volume likelyexceeded 2 to 3 million cubic kilometers, says Chenet. The entirevolcanic episode that created the traps took place over about onemillion years. The source of the massive lava flows is thought to havebeen the surfacing of a plume of hot material from deep in the Earth'smantle.