A faraway supernova explosion may have contributed to a minor mass extinction here on Earth 2.59 million years ago, a new study suggests. Fast-moving, charged particles called cosmic rays that were blasted out by asupernova may have played a role in the climatic changes that apparently led to a die-off at the end of the Pliocene epoch and the start of the Pleistocene, researchers said. "Africa dried out, and a lot of the forest turned into savannah. Around this time and afterwards, we started having glaciations — ice ages — over and over again, and it's not clear why that started to happen," study co-author Adrian Melott, of the University of Kansas, said in a statement. "It's controversial, but maybe cosmic rays had something to do with it." [Wipe Out: History's Most Mysterious Extinctions] Melott and his colleagues — led by Brian Thomas, of Washburn University in Kansas — conducted computer simulations that modeled how supernovas might affect Earth's climate and biosphere.