The small blue-and-white cap seen surrounded by rubble is all that seals the Kola Superdeep Borehole, which extends 40,230 feet (12,262 meters) deep. WIKIMEDIA/(CC BY-SA 4.0)
Key Takeaways
The Kola Superdeep Borehole, located in Russia, is the world's deepest man-made hole, reaching a depth of 40,230 feet (12,262 meters) or 7.6 miles (12.2 kilometers), surpassing the depth of the Mariana Trench and the height of Mount Everest.
The drilling project, initiated by the Soviets in 1970, revealed unexpected findings such as the absence of the "Conrad discontinuity" transition from granite to basalt, the presence of liquid water at unexpected depths, and microscopic fossils from single-celled marine organisms dating back 2 billion years.
Despite the significant depth achieved, the drilling faced challenges like increasing temperatures and rock densities, leading to the project's discontinuation in 1992, with the hole being sealed in 2005.
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. It resulted in the deepest hole in the world.
https://science.howstuffworks.com/engineering/civil/kola-superdeep-borehole.htm