Millennia of chaos may have finally brought down the dinosaurs

Wednesday, December 7, 2011

Millennia of chaos may have finally brought down the dinosaurs

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.

dinosaur fossils

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.

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.

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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