(Phys.org)—A team of researchers with members from several institutions in China and the U.S. has found evidence of uncharacteristic shoaling before, during and after the great die-off 250 million years ago and suggest it could be the cause of so many species going extinct. In their paper published in Proceedings of the National Academy of Sciences, the team describes evidence they found in rocks in Canada and Japan that suggests at least part of the great die-off was due to excess toxic sulphides permeating the world’s oceans.