It's pretty humbling to know that we actually understand more about galaxies that are billions of lightyears away than we do about the inside of own planet. In an effort to learn more about the depths of the Earth, the Soviet Union launched a mission to see how deeply we could drill into the Earth back in 1970.
The result of this project is the Kola Superdeep Borehole. Pictured below is where the drill from the project is now stored.
Soviet scientists drilled into the Earth's crust for 24 years. By the time the project was stopped, they had created a borehole into the Earth's surface that was about 7.5 miles deep. To put that into perspective, the deepest point in the ocean is only 6.8 miles down.
This is what the actual borehole looks like today. It's been welded shut to prevent anything (or anyone) from accidentally being thrown down into it.
How much did we learn from all of that drilling? Quite a bit, actually. At the 4-mile marker, scientists discovered microscopic fossils, along with prehistoric water sources.
By the time drilling stopped, the borehole had reached a blistering temperature of 356 degrees Fahrenheit.
Above is what the drilling facility looks like today.
The facility, now forgotten, was once a point of national pride. It even made it onto a postage stamp.
(via IFL Science)
But if seven miles sounds like a lot, further research suggets that the Soviets had another 4,000 miles to go before they reached the core. It was still a valiant effort.