Professors revise theory of dinosaurs' extinction
After years of detective work, University geosciences professor Gerta Keller and her colleagues have found that an intensive period of volcanic eruptions and a series of asteroid impacts likely ended the dinosaurs' reign on Earth, challenging the dominant theory that a single cataclysmic asteroid hit caused their extinction.Though an asteroid or comet could have struck Earth at the time of the dinosaur extinction, it most likely was, Keller said, "the straw that broke the camel's back" and not the sole cause.For more than a decade, scientists have believed the Chicxulub crater ? submerged off Mexico's Yucatan peninsula and and more than 110 miles wide ? was the remnant of the dinosaur-killing event.The time of the dinosaur extinction is known as the Cretaceous-Tertiary boundary (K-T). Keller's team, working on the problem since the Chicxulub was identified as the K-T impact crater, accumulated data and evidence from more than 100 localities that simply did not fit the popular K-T impact theory."We wanted to find out just what the kill-effect of this impact was, how quickly the mass dying occurred and whether there were environmental changes preceding it that may have contributed to the mass extinction," Keller said.Keller's findings revealed that the asteroid which formed the Chicxulub crater crashed 300,000 years before dinosaurs died out.