Scientists, politicians and officials met several thousand feet below the surface Monday for a groundbreaking ceremony at a new laboratory in an old South Dakota gold mine. It will be the world's deepest underground science lab — with its depths plunging as far as 8,000 feet below the surface — and well-positioned for scientists to study a secretive cosmic substance called dark matter. Being so far inside the Earth will shield experiments from cosmic rays as they try to prove the existence of dark matter, which is believed to contain no atoms yet make up nearly 25 percent of the universe.  (Text from The Daily Briefing)