Why the USSR Stopped Drilling at 12,262 Meters Came Down to an Unexpected Limit

12,262 meters down, the Soviet SG-3 Kola Superdeep Borehole set the world record for the deepest hole ever drilled after a project that began in 1970 aiming for 15 kilometers. The effort ultimately ended in 1992 when extreme heat and pressure made the rock behave plastically, warping and squeezing the borehole shut despite specialized rigs […]