The Kola Superdeep Borehole
For 24 years, Soviet scientists dug deeper into the Earth’s surface than anyone had ever done before. The result was the Kola Superdeep Borehole located on the Kola Peninsula in Russia.
The ambitious project began in the 1970s, and scientists in the former Soviet Union began to drill a hole that was just 9-inches (22.9 cm) in diameter. The hole eventually extended 7.5 miles (12.1 km) into the Earth’s crust, farther than the deepest point in the ocean, Challenger Deep in the Marianas Trench in the Pacific Ocean at 6.8 miles (10.9 km).