Over forty years ago, researchers in the Soviet Union began an ambitious drilling project whose goal was to penetrate the Earth's upper crust and sample the warm, mysterious area where the crust and mantle intermingle– the Mohorovičić discontinuity, or "Moho."
So deep is this area that the Russian scientists had to invent new ways of drilling, and some of their new methods proved quite inventive.
But despite the valiant effort which spanned several decades, the Russians never reached their goal, and many of the Earth's secrets were left undiscovered.
The work done by the Soviets did, however, provide a plethora of information about what lies just beneath the surface, and it continues to be scientifically useful today. The project is known as the Kola Superdeep Borehole.
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