That's the depth at which scientists discovered a new species of worm, dubbed Halicephalobus mephisto in honor of Faust's demon Mephistopheles. The worm, reported this week in the journal Nature, is the deepest living multicellular organism ever found.
Onstott and his colleagues have been searching for subsurface life for 15 years, focusing on the ultra-deep mines of South Africa, which penetrate more than 1.8 miles (3 km) into the Earth. They and other teams of scientists have found that life has very deep roots, with single-celled organisms found miles underground. Some of these organisms are quite extreme: One 2008 study found life thriving a mile under the seafloor, surviving in temperatures between 140 and 212 degrees Fahrenheit (60 and 110 degrees Celsius). [Read Extremophiles: World's Weirdest Life]
But finding the multicellular, 0.02-inch-long (0.5 millimeters) H. mephisto is a different story. The worm, or nematode, lives in fluid-filled rock fractures, where it grazes on bacteria, Onstott told LiveScience.