THIS IS THE BIGGEST HOLE in to the Earth, anywhere. It was drilled in Russia, and are 40,226 feet deep {7.62 miles}. It was drilled for scientific research. They found that the temperature did not increase at the same rate as it decreases with higher altitude {40,000 feet of altitude above ground is more or less constant 35 to 40 below F {40 below F is about -45C} There was also large leaks of Hydrogen { H } in to the hole from the surrounding ground. They were speculating how to harness it for fuel.