Mankind will probably never take a journey to the center of the Earth (sorry, Jules Verne), but we have drilled down some of the way, at least. From 1970 to 1994, Soviet engineers drilled into the Earth's crust, ultimately reaching a depth of 7.6 miles (12.3 km) via a hole only 9 inches (23 cm) wide. That might not seem like much, considering the fact that the average distance to the planet's core is 3,959 miles (6,371 km), but it's very impressive from a scientific standpoint. The Kola Superdeep Borehole has helped researchers discover that the layer of granite rock extends far deeper into the Earth's crust than scientists has previously theorized. The drilling project has also proved the existence of two billion-year-old microscopic plankton fossils down in the depths of the Earth's crust. If you want a close-up look at the deepest artificial point on Earth -- or, more accurately, the circular metal cover above it -- you'll have to travel on some rough roads to the little village of Zapolyarny in the northwestern corner of Russia.
Crust, mantle, core:
- At the boundary between the Earth's crust and the mantle underneath it, temperatures can reach 752 degrees Fahrenheit (400 degrees Celsius). (
- Mars, Venus, and Mercury also have outer crusts, but Jupiter, Saturn, Uranus, and Neptune are mostly gas, and thus do not have a hard outer shell.
- The Earth's crust is around 25 miles (40 km) deep, which makes it roughly 1 percent of the entire volume of the planet.