In the 70s, Russia and the United States were locked in a race to see who can dig the deepest hole on the ground.

The result was the Kola Superdeep Borehole which, at 40,230 feet or 12.2 kilometers deep, is the deepest man-made hole and the deepest artificial point on Earth. The goal was to drill deep into the crust and maybe reach the mantle to study the planet's inner processes and makeup, understand the plate tectonics, and find out the age of Earth.

The borehole situated in the Kola Peninsula in Russia was deep, but it did not reach the mantle. The project was halted in the early 90s following the collapse of the Soviet Union.

What The Soviet Researchers Found

Aside from setting world records, the Kola Superdeep Borehole led to several discoveries.

Prior to drilling, scientists expected a granite-basalt boundary at around 7 kilometers. However, the project proves that this was not the case.

The second major discovery is the presence of water.

"When the Russians started to drill they claimed they had found free water — and that was simply not believed by most scientists," explained Uli Harms of the International Continental Scientific Drilling Program to the BBC. "There used to be common understanding among Western scientists that the crust was so dense 5km down that water could not permeate through it."

Researchers also found evidence of biological activity in rocks that are estimated to be about 2 billion years old. They discovered microscopic fossil in some organic compounds that were surprisingly well-preserved despite the enormous pressure and intense temperature.

At the bottom of the hole, the temperature was measured at 180 degrees Celsius, which is higher than the expected 100 degrees Celsius. The researchers also reported a decrease in rock density after 4.5 kilometers.

Journey To The Center Of The Earth

Today, there is another effort to dig deep into the earth and reach the mantle. The Project MoHole To The Mantle (M2M) aims to drill through the seabed where rge crust is about 6 kilometers deep and recover a sample from the mantle.

"If we have a better knowledge of what the mantle is and how the mantle behaves, we have better knowledge of volcanoes and earthquakes, and better knowledge of how the planet as a whole works," said Benjamin Andrews, a research geologist, in an interview with The Smithsonian Magazine.