How the Soviets dug the deepest hole in the World

In the Cold War '60s, as the space race heated up, another race began: to the center of the earth.

Well, perhaps the Soviets and Americans couldn't drill quite that deep, but they could try to get to the so-called Moho, more formally the Mohorovicic Discontinuity, the theorized but much-disputed boundary between the mostly solid crust and the magma-filled mantle.

After the launch of an American drilling program to reach the boundary, the Russians joined the race to drill the deepest hole in the world.

"Between 1960 and 1962, the combination of economic interest and national pride during the Space Race period inspired scientists of the Soviet Union to plan drilling a "Russian Mohole" whose objective was to reach the Mohorovicic Discontinuity before the American drilling program," Dean Dunn writing in the book, Science of the Earth.

The original goal was soon subsumed by the desire to learn more about how valuable ores formed, so the hopes of the Russian effort eventually landed in the middle-of-nowhere mining region, Pachenga. There, the Soviets drilled the deepest hole in the history of the world, more than 7 miles deep.

At the Kola Institute, pictured, the Russians drilled for more than 15 years to reach a crust depth of 40,226 feet, a record that's never been broken. But however successful the mission was as an exploration, the geological findings from the site remain murky and obscured by the way they emanated out of the fading Soviet scientific machine.

Stanford geologist and drilling expert, Mark Zoback, said that the Kola borehole was "an anomaly" even within the rather grandiose field of superdeep drilling projects.

Photo: Kola Institute