"Long before it's in the papers"
January 28, 2015


Report: dinos took repeat pounding before final exit

Oct. 26, 2006
Courtesy National Science Foundation
and World Science staff

Grow­ing ev­i­dence, pa­le­on­tol­o­gists say, shows that the di­no­saurs and their con­tem­po­rar­ies were not wiped out by one me­te­or im­pact, as is com­mon­ly as­sumed.

Rather, mul­ti­ple im­pacts, mas­sive vol­can­ism in In­dia and cli­mate changes con­s­pired to fin­ish off the great rep­tiles, ac­cor­d­ing to Ger­ta Kel­ler of Prince­ton Uni­ver­si­ty in Prince­ton, N.J., and col­leagues.

Paint­ing of an un­der­wa­ter scene from the Cre­ta­ceous pe­ri­od, the late era of the di­nosaurs, fea­tur­ing a long-necked ple­si­o­saur. Ple­si­o­saurs and mo­sa­saurs were the main pre­da­tors of the Cre­ta­ceous seas. A shark is al­so shown. Ple­si­o­saurs were not di­no­saurs but went ex­tinct along with them. (Paint­ing by Vlad­i­mir Krb, cour­te­sy North Da­ko­ta Ge­o­log­i­cal Sur­vey)

Many sci­en­tists have linked the die­off to a me­te­or-in­duced cra­t­er on Mex­i­co’s Yu­ca­tan Pen­in­su­la, called the Chic­x­u­lub cra­ter. 

In fact that crash may have been the les­s­er, and ear­li­er, of a se­ries of events that pound­ed Earth for more than 500,000 years, ac­cord­ing to Kel­ler’s team.

A fi­nal, much larg­er and still un­i­den­ti­fied im­pact 65.5 mil­lion years ago seems to have been the last straw, Kel­ler said, ex­ter­mi­nat­ing two-thirds of all spe­cies in one of Earth’s worst mass ex­tinc­tions. 

It’s that im­pact—not Chicx­u­lub—that left a fa­mous lay­er of the el­e­ment iri­d­i­um, found in rocks world­wide and thought come from space, Kel­ler ar­gued.

“The Chicx­u­lub im­pact alone could not have caused the mass ex­tinc­tion,” said Kel­ler, because the im­pact oc­curred 300,000 years before the die­off.

The sto­ry that seems to be tak­ing shape, ac­cord­ing to Kel­ler, is that Chicx­u­lub, though vi­o­lent, ac­tu­al­ly con­spired with pro­longed, huge erup­tions of the Dec­can Flood Basalts in In­di­a to nudge spe­cies to­wards the brink. A sec­ond huge me­te­or crash fi­nal­ly pushed them over.

The Dec­can vol­can­ism re­leased copious green­house gas­es that fueled glo­bal warm­ing, she ad­ded, so that by the time of Chicx­u­lub, the oceans were 3 to 4 de­grees warm­er at the bot­tom. “On land it must have been 7-8 degrees warmer.”

But where is the second crat­er? “I wish I knew,” said Kel­ler, who pre­sented the find­ings this week at the an­nu­al meet­ing of the Ge­o­log­i­cal So­ci­e­ty of Amer­i­ca in Phil­a­del­phia.

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Growing evidence shows that the dinosaurs and their contemporaries were not wiped out by one meteor impact, as is commonly assumed, according to paleontologists. Gerta Keller of Princeton University in Princeton, N.J., and colleagues announced that new studies indicate multiple meteor impacts, massive volcanism in India and climate changes conspired to finish off the dinosaurs about 65 million years ago. Many scientists have linked the dieoff to a meteor-induced crater on Mexico’s Yucatan Peninsula, called the Chicxulub impact. But that impact may have been the lesser and earlier of a series of meteor impacts and volcanic eruptions that pounded Earth for more than 500,000 years, according to Keller’s team. A final, much larger and still unidentified impact 65.5 million years ago seems to have been the last straw, said Keller, exterminating two-thirds of all species in one of Earth’s worst mass extinctions. It’s that impact—not Chicxulub—that left a famous layer of the element iridium, found in rocks worldwide, and believed come from space, Keller believes. That layer is believed to mark the impact that finally ended the Age of Reptiles. “The Chicxulub impact alone could not have caused the mass extinction,” said Keller, “because this impact predates the mass extinction.” But where is the other crater? “I wish I knew,” said Keller. She presented her findings this week at the annual meeting of the Geological Society of America in Philadelphia.