In this July 6, 2012 photo provided by Courtney Sprain, Paul Renne collects a volcanic ash sample from a coal bed in Montana, within a few centimeters of the dinosaur extinction layer.

 

              In this July 6, 2012 photo provided by Courtney Sprain, Paul Renne collects a volcanic ash sample from a coal bed in Montana, within a few centimeters of the dinosaur extinction layer.
In this July 6, 2012 photo provided by Courtney Sprain, Paul Renne collects a volcanic ash sample from a coal bed in Montana, within a few centimeters of the dinosaur extinction layer. Two studies published Thursday, Feb. 7, 2013 in the journal Science better explain the Earth-shaking consequences of a catastrophic cosmic collision 66 million years ago when a comet or asteroid smashed into the Gulf of Mexico. The crash seemed to end the reign of the dinosaurs, according to a study by led Renne. And it gave way to the age of mammals that probably started with a cute squirrel like critter and eventually led to us, a second study said. (AP Photo/Courtney Sprain)