A Cold War race to the crust
The Kola Superdeep Borehole is the deepest artificial point on Earth. It began on May 24, 1970, on the Kola Peninsula in the Soviet Union as a purely scientific endeavor to probe the Earth's crust. Unlike the space race, this contest sought to go as deep as possible, with a target depth of 15,000 meters. The project used a specialized Uralmash-15000 drilling rig. Instead of rotating the entire 12-kilometer drill string, engineers designed a system where only the drill bit at the bottom turned, powered by the flow of pressurized drilling mud.
The main borehole, SG-3, reached a true vertical depth of 12,262 meters (40,230 feet) in 1989. This is deeper than the Mariana Trench and surpasses the combined height of Mount Everest and Mount Fuji. The hole itself is surprisingly narrow, only 23 centimeters (9 inches) in diameter at the surface. Drilling stopped in 1992 because the temperature at that depth reached 180°C (356°F), far hotter than the 100°C that scientists had predicted. At this heat, the rock began to behave like a plastic, and the equipment could not function. The facility was officially closed in 2005, and today the hole is sealed with a welded metal cap amid the ruins of the research station.
Unexpected discoveries
The borehole produced a wealth of geological data. One of the biggest surprises was the absence of a predicted transition from granite to basalt rock at around 7 kilometers deep. This feature, known as the Conrad discontinuity, was a long-held geological theory based on seismic wave data. The Kola drill found only granite, leading to the understanding that the seismic shift was due to metamorphic changes in the rock, not a change in rock type.
Scientists also made two astonishing discoveries. First, they found liquid water at depths between 3 and 6 kilometers. This water was not expected, as the immense pressure should have made the rock impermeable. It is mineralized water—hydrogen and oxygen atoms squeezed from rock crystals and trapped beneath an impermeable layer. Second, at a depth of about 6.7 kilometers, researchers discovered microscopic fossils of 24 species of single-celled marine organisms (plankton). These 2.7-billion-year-old microfossils were remarkably well preserved inside organic compounds that protected them from the extreme temperature and pressure.
The "unexplained sounds" mentioned in the project's lore are an urban legend known as the "Well to Hell hoax." A fabricated story from the 1990s claimed a microphone lowered into the hole recorded the screams of the damned. No such recordings were ever made by the scientific team; the myth likely came from misinterpretations of seismic and acoustic measurements of rock stress.