Scientists widely accept that the extinction of the dinosaurs was triggered when a massive object smashed into Earth and touched off a global ice age that wiped out as many as three-quarters of all species. The question, however, is where that object originated. Harvard physicists believe they may have the answer, and their theory may prompt scientists to re-evaluate the decades-old conventional wisdom about one of the most mysterious substances in the universe: dark matter. Though the exact nature of dark matter remains unknown, physicists have been able to infer its existence based on the gravitational effect it exerts on ordinary matter. Though dark matter is otherwise believed to be non-interacting, theoretical physicists Lisa Randall, the Frank B. Baird Jr. Professor of Science, and Matthew Reece, assistant professor of physics, earlier this year suggested that a hypothetical type of dark matter could form a disk of material that runs through the center of the galaxy. If the solar system, as it orbited the center of the galaxy, were to move through that disk, they theorized that the gravitational effects from the dark matter might be enough to dislodge comets and other objects from what’s known as the Oort Cloud and send them hurtling toward Earth. More via Harvard Gazette.