It’s 3,958 miles to the center of the Earth, and there’s a lot to explore along the way. You pass through multiple stages of rock, the oceanic crust, the upper mantle, lower mantle, and so on. To put this in perspective, James Cameron got his Challenger Deep sub only 6.8 miles down in 2012.
For more info, take a look with this graphic from the BBC. You can see the depth of human discovery underground, including the deepest mines, laboratories, nuclear explosions, and radio broadcasts. You also get a sense of what we don’t know about the deep. Cameron got to 11,000 meters, and the center of the Earth is at 6.3 million meters down. Humanity, it’s often said, knows much more about what’s above than below, though there are efforts to find out more. A British team is drilling off the coast of Costa Rica, hoping to reach the mantle layer, which starts at about 30,000 meters below the surface.
The leader of the project, Damon Teagle, told CNN the project was the most challenging “in the history of Earth science.” It certainly sounds like it–the hole is just 11 inches wide. “It will be the equivalent of dangling a steel string the width of a human hair in the deep end of a swimming pool and inserting it into a thimble 1/10 millimeters wide on the bottom, and then drilling a few meters into the foundations,” Teagle said.
As for what is known, the graphic shows the maximum depths of earthquakes, the end of the upper mantle, the beginning of the outer core (at 2.9 million meters deep), and finally the center, where the pressures are incredible. The BBC says being there would be like having 47,000 elephants on your head. Not nice.