The Kola Superdeep Borehole remains one of humanity’s most ambitious scientific drilling projects. Begun in the 1970s by Soviet scientists on the Kola Peninsula in northwestern Russia, the borehole ultimately reached a depth of 12.2 kilometers (7.6 miles)—the deepest point ever drilled into Earth’s crust. The goal wasn’t oil or minerals, but pure science: to study the composition and structure of the continental crust. What researchers found surprised them. Temperatures at depth exceeded 180°C (