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2015-10-01. Volcano-asteroid combo may have done in the dinosaurs.

posted Oct 4, 2015, 10:04 AM by Alan Gould   [ updated Oct 14, 2015, 4:15 PM ]
By Sid Perkins, Science. For GSS A Changing Cosmos chapter 1 and Life and Climate chapter 9. Excerpt: Scientists have for decades hotly debated what killed the dinosaurs. One long-held hypothesis blames immense and long-lasting volcanic eruptions that drastically altered Earth’s climate. Another more recent hypothesis suggests that the dino die-offs occurred after a massive asteroid hit the planet near the Yucatán Peninsula. Now, research finds that the extraterrestrial impact may have led to increased volcanism in the Indian subcontinent, providing a double whammy that took out Tyrannosaurus rex and his kin. ...The new study finally provides dates for those eruptions. Using an argon-argon radioactive dating technique, a team led by geochronologist Paul Renne of the University of California, Berkeley, sampled materials from ancient lava layers at sites in the Deccan Plateau of central and western India. They found that the Deccan eruptions started at least 173,000 years before the asteroid hit and continued for at least 500,000 years after the impact. What’s more, the researchers were able to determine the size and strength of each major eruption, based on lava flow estimates. Before the impact, the eruptions produced about 71,000 cubic kilometers of lava—an average rate of about 400 million cubic meters each year. But starting about 50,000 years after the asteroid impact, Deccan volcanoes and fissures began spewing lava at an average rate of about 900 million cubic meters per year, the researchers report online today in Science. ...How the asteroid impact half a world away from India bumped up lava production is a mystery, Renne says. He speculates that its effects rippled along the boundaries of nearby tectonic plates until they reached the volcanoes, expanding the size of subterranean magma chambers and thus increasing the volume of magma they could spew during any given eruption. Not all scientists are convinced.  ...Ironically, by more closely linking the date of the impact with the increase in Deccan volcanism, Renne and his team may have made it more difficult to tease out the relative contribution of each phenomenon to the die-offs, Melosh says. “These findings will add greatly to the controversy of volcanism versus impact.”  http://news.sciencemag.org/climate/2015/10/volcanoes-and-asteroid-strike-may-have-done-dinosaurs?utm_campaign=email-news-weekly  See also http://news.berkeley.edu/2015/10/01/asteroid-impact-volcanism-were-one-two-punch-for-dinosaurs/