The Soviet Union Dug the Deepest Hole on Earth 55 Years Ago. It Might Hold the Key to Our Green Energy Future.

3 min readHere’s what you’ll learn when reading this story:The Soviet Union began excavating the Kola Superdeep Borehole in 1970 with one mission: Dig as far as possible.The hole eventually reached 2,262 meters, or roughly 7.6 miles, before hot temperatures created a plastic-like rock flow that continuously sealed the hole. More than half a century after the project began, climate change is prompting scientists and engineers to rethink geothermal energy by drilling deeper to reach rocks hot enough to superheat water and generate renewable power.On May 24, 1970, drilling began on a then-nondescript borehole located on the Kola Peninsula. This spit of land rests along the border of Norway and Russia, but in 1970, the peninsula—once the domain of the indigenous Sami people—belonged to the Soviet Union. And as part of the year-long celebration of what would have been Vladimir Lenin’s 100th birthday, the world superpower undertook a variety of projects to show off its might.This man-made hole was one of them.When physical, financial, and technological constraints ended the project in 1992, the Kola Superdeep Borehole (SG-3) had reached a record depth of 12,262 meters, or about 7.6 miles. Though still more than 3,700 miles from Earth’s core, the borehole marked humanity’s deepest penetration into the planet. According to Orion Magazine, the drill ventured past deposits of metals (copper, nickel, and magnetite) and onward toward rocks that resembled samples recovered from the Moon, until it finally hit 2.5 billion-year-old rocks filled with fossils of microscopic plankton.Then, things got hot. According to a scientific review of ultra-deep drilling published in February 2026 in the journal Communications Earth & Environment, temperatures at the bottom of the borehole reached 212 degrees Celsius, creating a “plastic rock flow that repeatedly sealed the hole.”“The SG-3 well fundamentally reshaped understanding of continental crustal structure and deep geologic processes,” the authors wrote. “Despite not penetrating the Moho [boundary between Earth’s crust and mantle], SG-3 yielded the most extensive direct dataset on the crystalline continental crust.”Although SG-3 was a scientific oddity at the time—and the subject of a strange hoax where people believed you could record the voices of the damned in hell from inside it—data collected from boreholes such as this one can be immensely important for understanding the heat (i.e. energy) trapped beneath our feet. Next-generation enhanced geothermal systems, or EGS, dig deeper than conventional wells and rely on fracking techniques to inject high-pressure water that soaks up the heat of the Earth and transports it back to the surface in the form of usable green energy.The U.S. Energy Information Administration (EIA) says the western U.S. has the greatest potential for geothermal energy, since tectonic boundaries help bring a lot of the Earth’s heat closer to the surface. The administration also reports that the Great Basin alone could potentially tap into 135 gigawatts (GW) of electrical generation (good news for the region as rivers that once provided electricity begin to dry up). By comparison, the U.S. currently only has 4 GW of conventional hydrothermal power, which is roughly 0.4 percent of our total electricity output. Later this year, a large-scale EGS system will send power to the grid in Utah, and other potential superhot rock hotspots have been found in places like west Texas and central Oregon. Luckily, these projects won’t have to dig nearly as deep as SG-3 to reach temperatures as hot as 400 degrees Celsius.Today, the Kola Superdeep Borehole lies abandoned in what’s now considered one of the most “poisoned spots on Earth,” where decades of industrial contamination have devastated a once-thriving landscape. With luck, lessons from SG-3 could help scientists and engineers develop cleaner energy—and spare other places a similar fate.Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.