The deepest hole in the earth is the Kola Superdeep Borehole in northwestern Russia, which extends 12.2 km deep. Deep boreholes like this one can tell scientists a lot about the earth’s interior.

The Earth's layers - crust, mantle, and core - present extreme pressures and temperatures that existing equipment cannot withstand. The Kola Superdeep Borehole, the deepest drill to date ...