The Four-Inch Lifeline

On August 5, 2010, the San Jose copper mine in Chile collapsed, trapping 33 miners 2,300 feet underground. For 17 days, no one on the surface knew if they were alive. Then a narrow borehole, just four inches wide, broke through to their cavern. A note came back tied to a drill bit: "We are fine in the shelter, all 33 of us."…