The truth about the deepest hole in the world

Back when you were a kid, your grandpa joked that if you dug deep enough underground, you might carve a hole all the way to China. This lie might've fueled you to keep going (which was good for his garden, if not your hands), but the chances are, your hours of effort probably only got a few feet deep. Hardly the bottomless pit you might've hoped for. 

Scientists, on the other hand, have gone a lot deeper. Over the course of the 20th century, experts from all over the world have dug, dug, dug in their quest to reach Earth's mantle, the bulk of rock that awaits beneath the Earth's crust, blankets its flaming hot core, and contains the geological record of Earth's history. If humans can access the mantle, they'll also have a more solid grasp of earthquakes, volcanoes, and everything else happening on the globe. This quest for depth has led to all kinds of terrifyingly deep holes punching through the Earth, but the deepest of them all can be found in Murmansk, Russia.

In Russia, they dig deep

Say hello to the Kola Superdeep Borehole, pictured above, the deepest hole on Earth.

What, it doesn't look like a hole to you? Listen, that cap is there to save your ankle, because while Smithsonian says this hole has only a 9 inch diameter at its base, it goes down 7.5 miles into the Earth, or 40,230 feet. That sounds deep, and it is deep — deep enough to uncover Precambrian, microscopic plankton fossils, which was a win for science! — it still descends only halfway to the mantle. Dang. As with so many scientific quests in the 20th century, the Kola Superdeep Borehole was a result of (sigh) Cold War tensions, as Mental Floss explains. The U.S.A. dropped their own "let's reach the mantle" dig, labeled Project Mohole, in 1958, leading to the Soviet Union to pick up the ball four years later. Following this, the Russians plugged away at their hole for over twenty years ... until a flood of demonic monsters climbed out of the pit and ate them. Just kidding, about the last part. The real problem was the fact that in 1992, the drillers hit crazy hot temperatures of 356 degrees Fahrenheit, which totally messed up their equipment. Bummer. Nonetheless, the Kola Superdeep Borehole remains one of the great scientific achievements in Russian history, according to Atlas Obscura, and you can still visit it today.

Here's another weird twist: while the Kola Superdeep Borehole certainly is the deepest man-made hole on Earth, it's not the longest. That honor goes to an oil well drilled in 2008, according to Gulf Oil and Gas, in Qatar. The disparity comes down to Earth's general unevenness. Basically, while the Qatar hole is technically over 100 feet longer, the Russian hole goes far deeper underground.