While the United States and the USSR were focusing on space exploration during the great space race of the 1960s, the Americans and Soviets were also vying for supremacy of another kind: one to the center of Earth, or at least as close to it as possible.
In 1958, Americans launched Project Mohole, a plan to retrieve a sample from Earth's mantle by drilling to the bottom of the ocean off Guadalupe Island, Mexico. With funds from the National Science Foundation, they drilled 601 feet (183 meters) into the seabed before the project was pulled in 1966 by the U.S. House of Representatives.
In 1970, the Soviets launched their attempt, drilling into Earth in Murmansk, Russia, just outside the Norwegian border near the Barents Sea. It's known as the Kola Superdeep Borehole and it was more successful, penetrating much deeper into Earth and collecting samples that still wow scientists today.
Why dig so deep into the Earth? "To address key scientific questions" that could give answers to some of science's biggest mysteries about our planet, says Dr. Ulrich Harms. Harms is the director of the German Scientific Earth Probing Consortium at the German Research Centre for Geosciences in Potsdam, Germany. He's visited the Kola Borehole, browsed the repository of core samples and even laid hands on the now-defunct wellhead.
And while the Kola Superdeep Borehole never reached beyond Earth's crust, it remains the deepest man-made hole in the world.