What is the deepest artificial hole ever drilled into Earth?

The Kola Superdeep Borehole is the deepest artificial hole ever drilled into Earth, reaching 12,262 metres.

The Soviet Union began drilling the project on the Kola Peninsula in 1970 to study Earth’s deep crust. The deepest branch, SG-3, reached its record depth in 1989. Drilling stopped because temperatures and technical difficulties became greater than expected.

The project revealed that the deep crust was hotter than predicted and contained water in fractured rocks. It also found that the boundary between granite and basalt was not a simple, universal layer as some models had suggested. Instead, seismic changes reflected complicated changes in rock properties.

The Kola borehole is often confused with the deepest mine. Mines descend vertically for access to ore, whereas Kola was drilled primarily for scientific investigation. It remains famous because humans have penetrated only a small distance compared with Earth’s roughly 6,371-kilometre radius.