Researchers believe huge underwater volcanic eruptions were part of last extinction period

September 10, 2012 – GEOLOGY – Popular opinion holds that an asteroid struck the Earth 65 million years ago, hustling out the Age of Dinosaurs and allowing the mammals – us – to rise. But new research now paints another picture – with the University of Washington indicating that a separate extinction came shortly first, triggered by volcanic eruptions that warmed the planet and killed life on the ocean floor. They suggest that by the time of the asteroid impact, life on the seafloor – mostly species of clams and snails – was already perishing, because of the effects of huge volcanic eruptions on the Deccan Plateau, in what is now India. The well-known dinosaur extinction event is believed to have been triggered by an asteroid at least six miles in diameter slamming into Mexico’s Yucatán Peninsula. Thomas Tobin, a UW doctoral student in Earth and space sciences, said: ‘The eruptions started 300,000 to 200,000 years before the impact, and they may have lasted 100,000 years.’ During the earlier extinction it was primarily life on the ocean floor that died, in contrast to the later extinction triggered by the asteroid impact, which appeared to kill many more free-swimming species. The eruptions would have filled the atmosphere with fine particles, or aerosols that initially cooled the planet. But, more importantly, the eruptions also would have spewed carbon dioxide and other greenhouse gases to produce long-term warming that led to the first of the two mass extinctions. –Daily Mail