How low can you go?

What is the deepest hole ever dug?

We asked what Russian scientific achievement, considered a geological landmark, produced the deepest hole ever dug.

The Kola Superdeep Borehole, located in Russia's Kola Peninsula, reached a final depth of more than 12 kilometers.

The project began in the early 1970s as a strictly scientific measure. Over the next three decades, Russian teams employed exotic drilling techniques in an effort to breach the 12-kilometer barrier. The Borehole's depth is as much a testament to perseverance as it is to technical prowess.

A similar U.S. endeavor, dubbed Project Mohole, reached less than a kilometer in depth before political and technical obstacles prompted Congress to cut funding in 1966, only five years after the project began. Project Mohole sought to penetrate the Earth's crust at its thinnest--below the ocean's surface.

The only western excavation that came close to the Borehole's depth--and was briefly the record holder for the world's deepest manmade hole--is the Bertha Rogers oil well in Oklahoma. The well reached a final depth of more than 9.5 kilometers before it impacted a molten sulfur deposit in 1974. Naturally, the Bertha Rogers oil well was part of a commercial venture and provided relatively few scientific discoveries.

The Kola Superdeep Borehole eventually overtook the Rogers well and has outpaced all competing efforts to remain one of the "deepest" scientific achievements in history.