On the remote Kola Peninsula in northwestern Russia, amid the rusting ruins of an abandoned scientific research station, is the deepest hole in the world. Now covered and sealed with a welded metal plate, the Kola Superdeep Borehole, as it’s called, is a remnant of a largely forgotten Cold War race that aimed not at the stars, but at Earth’s interior.
A team of Soviet scientists began drilling at Kola in the spring of 1970, with the goal of penetrating as far into Earth’s crust as their technology would allow. Four years before the Russians started punching their way into the Kola crust, the United States had given up on its own deep-drilling program: Project Mohole, an attempt to bore several miles through the Pacific seafloor and retrieve a sample of the underlying mantle. Mohole fell far short of its target, reaching a depth of just 601 feet after five years of drilling under more than 11,000 feet of water.
The Soviets were more persistent. Their work at Kola continued for 24 years — the project outlived the Soviet Union itself. Before drilling ended in 1994, the team hit a layer of 2.7-billion-year-old rock, almost a billion years older than the Vishnu schist at the base of the Grand Canyon. Temperatures at the bottom of the Kola hole exceeded 300 degrees Fahrenheit; the rocks were so plastic that the hole started to close whenever the drill was withdrawn.
While the researchers at Kola bored patiently downward, their counterparts in the space race sent dozens of craft heavenward: as far as the moon, Mars and beyond. By the early 1990s, when the Kola effort began to stall, the Voyager spacecraft had already passed beyond Pluto’s orbit. And the depth of the Kola hole after 24 years of drilling? About 7.6 miles — deeper than an inverted Mount Everest and roughly halfway to the mantle, but still a minuscule distance, considering Earth’s 7,918-mile diameter. If Earth were the size of an apple, the Kola hole wouldn’t even break through the skin.
