The scientists say that evidence of the collision can be spotted
in telltale debris left by the impact. James Kennett,team member and geologist at the University of California in Santa Barbara,says a thin layer of sediment can still be found across North America.There are materials in the layer that“collectively provide very strong evidence that the layer was produced by this extraterrestrial impact,”he states. These materials include unusual forms of carbon as well as high concentrations of iridium,a metal rarely found on earth.Furthermore, there are no bones of mammoths or other large mammals above this layer of sediment.Earth's climate began to cool during this time,and Kennett and his team believe that the 1,000-year-long cold spell, known as the Younger Dryas event,was a result of the impact.The team theo1izes that the vast Laurentide Ice Sheet,which once covered much of North America,thawed and sent massive quantities of fresh water into the Atlantic Ocean.This water blocked a major current that had been bringing warming tropical waters from the south and thereby triggered the cooling.