Mpr News With Kerri Miller

More than 60 million years ago, an object the size of a small city barreled into planet Earth, traveling at more than 22,000 miles per hour. That meteoroid, many scientists believe, triggered a set of cataclysmic climate changes and natural disasters that led to the extinction of the dinosaurs. But what triggered the meteoroid? Lisa Randall, a particle physicist and bestselling author, tackles this question in her book, "Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe." Randall theorizes that the meteoroid was a comet that was dislodged from its orbit when the solar system passed through a disc of dark matter. If you're now wondering, "what's dark matter?", you're not alone. Dark matter is one of the great mysteries of modern science. Dark matter acts like matter, Randall said, "but what distinguishes it is that light just goes right through it. ... I wouldn't call it dark — I would call it transparent." "Billions of dark mat