What is the deepest hole ever dug?
I'm not sure of the exact depth, but the deepest that I've heard of was a hole drilled by the Soviet Union in an attempt to penetrate the crust and reach the upper mantle. The hole was near Murmansk, Russia, and reached a reported depth of approximately 12 kilometers. They didn't make it to the mantle. The United States also made an effort (the Deep Crustal Drilling Program) which was also unsuccessful.
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