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November 23, 2011

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Millennia of chaos may have finally brought down the dinosaurs

Nov. 23, 2011
Courtesy of Princeton University
and World Science staff

It took not just a stray mete­orite, but a pum­me­ling on a scale barely ima­gin­able to finish off the dino­saurs some 65 mil­lion years ago, re­search­ers are re­port­ing.

The Prince­ton Uni­vers­ity sci­ent­ists tell of a double whammy of co­los­sal vol­can­ic erup­tions and me­te­or­ite strikes whose effects pound­ed the mighty beasts into fin­al sub­mission.

Their new re­search, which port­rays an Earth that was bare­ly hab­it­a­ble for half a mil­lion years, weaves to­ge­ther el­e­ments of two lead­ing the­o­ries on the mass ex­tinc­tion along with new de­tails. 

The re­sult is one, epic tale of un­re­len­ting chaos. 

Spe­cies of plank­ton­ic fora­mi­ni­fera, tiny shelled ma­rine crea­tures, got both few­er and smaller as the time of di­no­saurs' fi­nal de­mise drew near, re­search­ers say. The changes are thought to re­flect bru­tal cli­mat­ic con­di­tions. (Im­age cour­te­sy of Gerta Kel­ler)

One of these previous the­o­ries, which has been the pre­vail­ing one, holds that a single large me­te­or­ite felled the great rep­tiles along with many other crea­tures. The other theo­ry blames erup­tions alone.

A Prince­ton re­search team found that a trail of ti­ny, dead ma­rine or­gan­isms span­ning half a mil­lion years of­fers a time­line link­ing the mass ex­tinc­tion to large-scale erup­tions a pri­me­val vol­can­ic range once three times larg­er than France. The vol­ca­noes, known as the Dec­can traps, rose in west­ern In­dia.

A sec­ond re­search group uncov­ered traces near the Dec­can Traps of a me­te­or­ite that they said may have been one of a se­ries to strike the Earth around the time of the mass ex­tinc­tion. That, they said, could have pulled the plug on the few be­lea­guered sur­viv­ors of thou­sands of years of vol­cano-fueled mis­ery.

The first group re­ported this month in the Jour­nal of the Ge­o­log­i­cal So­ci­e­ty of In­dia that ma­rine sed­i­ments from Dec­can la­va flows show that the pop­ul­ation of a group of spe­cies known as plank­ton­ic fora­mini­fera plunged al­most to ex­tinc­tion in the thou­sands of years lead­ing up to the di­no­saur die-off. The fora­min­i­fera, which leaves ti­ny shells be­hind, are wide­ly used to gauge the fall­out of pre­his­tor­ic ca­tas­tro­phes be­cause they’re very sen­sitive to envi­ron­mental changes, said the re­search­ers, who were led by Prince­ton geo­sci­en­tist Gerta Kel­ler.

The de­struc­tion, they added, oc­curred in tan­dem with the larg­est erup­tion phase of the Dec­can Traps — the sec­ond of three — when the vol­ca­noes pumped the at­mos­phere full of cli­mate-altering car­bon di­ox­ide and sul­fur di­ox­ide. A less se­vere third phase of Dec­can ac­tiv­ity is be­lieved to have kept the Earth near­ly un­in­hab­it­a­ble for the next half a mil­lion years.

The other research group, based in Kel­ler’s lab, found ev­i­dence in In­di­an sed­i­ment of a me­te­or­ite strike from the time of the mass ex­tinc­tion. This and others like it could have purged the already de­vast­ated land­scape of the few, weak­ened spe­cies sur­viv­ing the Dec­can blasts, they said. That study ap­pears in the Oc­to­ber is­sue of the jour­nal Earth and Plan­e­tary Sci­ence Let­ters. 

Dinosaurs suc­cumb to chok­ing vol­can­ic gases in a pain­ting by Zina De­ret­sky

The same sed­i­ment — lo­cat­ed in Me­gha­la­ya, In­dia, more than 600 miles east of the Dec­can Traps — re­veals Earth in this pe­ri­od as a harsh land of ac­id rain and er­rat­ic tem­per­a­tures, the in­vesti­gators claim.

Kel­ler said the find­ings as a whole could put to rest the the­o­ry that the mass-ex­tinc­tion was due to just one large me­te­or­ite im­pact near Chicx­u­lub in pre­s­ent-day Mex­i­co. That im­pact — which oc­curred around the time of the sec­ond-phase Dec­can erup­tions — is thought to have been two mil­lion times more pow­er­ful than a hy­dro­gen bom­b and gen­er­at­ed an enor­mous dust cloud and gas­es that radic­al­ly changed the cli­mate. 

Kel­ler has long held that the Chicx­u­lub im­pact was­n’t bad enough to wipe out the scaly ani­mals that had lorded it over the land­scape. But the new work from her lab sug­gests the larg­est Dec­can erup­tions were that bad, or nearly so.

“Our work in Me­gha­la­ya and the Dec­can Traps pro­vides the first one-to-one cor­rel­ation be­tween the mass ex­tinc­tion and Dec­can vol­can­is­m,” said Kel­ler, who is lead au­thor of the Ge­o­log­i­cal So­ci­e­ty pa­per and co-authored the other pa­per with lead au­thor Bri­an Gertsch, now at the Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy. “But giv­en the en­vi­ron­men­tal in­sta­bil­ity caused by the mas­sive Dec­can erup­tions, an im­pact could easi­ly have killed off the few sur­vi­vor spe­cies at the end of the Cre­ta­ceous” era, which coin­cides with the dino­saurs’ de­mise.

Vin­cent Cour­tillot, a geo­phys­i­cist at Par­is Uni­vers­ity Di­de­rot who was­n’t in­volved in the Prince­ton work, called the find­ings an “im­pres­sive anal­y­sis.” Its sig­nif­i­cance is that it “was con­ducted in im­por­tant sec­tions near the vol­can­ic ac­tion, and not thou­sands of kilo­me­ters [miles] away as had been the case pre­vi­ous­ly,” said Cour­tillot, who led a team that re­ported in the Jour­nal of Geo­phys­i­cal Re­search in 2009 that Dec­can vol­can­ism oc­curred in three phases.

The new find­ings, he added, “pro­vide sup­port for the idea that car­bon and sul­fur di­ox­ide emis­sions were the prin­ci­pal agents of en­vi­ron­men­tal change and stress.”

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A cosmic one-two punch of colossal volcanic eruptions and meteorite strikes probably wiped out the dinosaurs 65 million years ago, according to two Princeton University reports. The research suggests the double catastrophe left the Earth nearly uninhabitable for half a million years. The proposal combines elements of two leading theories on the great reptiles’ extinction: the prevailing one, that one large meteorite was responsible, and an an alternative idea that blames volcanic eruptions. One Princeton research team found that a trail of tiny, dead marine organisms spanning half a million years offers a timeline linking the mass extinction to large-scale eruptions a primeval volcanic range once three times larger than France. The volcanoes, known as the Deccan traps, rose in western India. A second research group uncovered traces of a meteorite close to the Deccan Traps that they said may have been one of a series to strike the Earth around the time of the mass extinction. That could have wiped out the few species that remained after thousands of years of volcanic activity, they said. The first group reported this month in the Journal of the Geological Society of India that marine sediments from Deccan lava flows show that the population of a species known as planktonic foraminifera plunged almost to extinction in the thousands of years leading up to the dinosaur die-off. The foraminifera species, which leaves tiny shells behind, is widely used to gauge the fallout of prehistoric catastrophes, said the researchers, who were led by Princeton geoscientist Gerta Keller. The destruction, they added, occurred in tandem with the largest eruption phase of the Deccan Traps — the second of three — when the volcanoes pumped the atmosphere full of climate-altering carbon dioxide and sulfur dioxide. A less severe third phase of Deccan activity is believed to have kept the Earth nearly uninhabitable for the next half a million years. Another group based in Keller’s lab found evidence in Indian sediment of a meteorite strike from the time of the mass extinction that they said could have finished off the few, weakened species surviving the Deccan blasts. That study appears in the October issue of the journal Earth and Planetary Science Letters. The same sediment — located in Meghalaya, India, more than 600 miles east of the Deccan Traps —portrayed the Earth during this period as a harsh environment of acid rain and erratic global temperatures. Keller said the findings as a whole could put to rest the theory that the mass-extinction was due solely by a large meteorite impact near Chicxulub in present-day Mexico. That impact — which occurred around the time of the second-phase Deccan eruptions — is thought to have been two million times more powerful than a hydrogen bomb and generated an enormous dust cloud and gases that radically altered the climate. Keller has long held that the Chicxulub impact wasn’t bad enough to cause the mass extinction, but the new work from her lab suggests the largest Deccan eruptions were. “Our work in Meghalaya and the Deccan Traps provides the first one-to-one correlation between the mass extinction and Deccan volcanism,” said Keller, who is lead author of the Geological Society paper and second author of the other paper after lead author Brian Gertsch, now a postdoctoral researcher at the Massachusetts Institute of Technology. “But given the environmental instability caused by the massive Deccan eruptions, an impact could easily have killed off the few survivor species at the end of the Cretaceous,” Keller said. Vincent Courtillot, a geophysicist and professor at Paris University Diderot who wasn’t involved in the Princeton work, called the findings an “impressive analysis.” Its significance is that it “was conducted in important sections near the volcanic action, and not thousands of kilometers [miles] away as had been the case previously,” said Courtillot, who led a team that reported in the Journal of Geophysical Research in 2009 that Deccan volcanism occurred in three phases. The new findings, he added, “provide support for the idea that carbon and sulfur dioxide emissions were the principal agents of environmental change and stress.”