A team of geoscientists have discovered a breed of tiny worms living around a mile below the surface of the earth. It’s already sparking speculation that this could show another way life might be able to exist on other planets.

The Halicephalobus mephisto worm was discovered in a South African gold mine. It’s barely one-fiftieth of an inch long, but that still represents a significant breakthrough: until now, only single-cell organisms had been known to exist anywhere close to that deep.

The worms have very much adapted to the unusual conditions, which can reach more than 100 degrees Fahrenheit. They feed on subsurface bacteria and reproduce asexually. Although they live in the water in earth fractures far below the surface, they have not been found closer to the surface of the mine.

Despite its tiny size, the worm is comparatively huge: Tullis Onstott, who led the team, noted it was 10 billion times bigger than the bacteria it feeds on, and likened the discovery to “finding Moby Dick in Lake Ontario.”

The discovery may undermine the theory that if there is life on Mars, it must be a simple microbe. It now becomes more plausible that complex life may have developed on Mars when the planet’s conditions were more favorable, then moved deep underground to survive and even evolve.

(Picture credit: Gaetan Borgonie/University Ghent, Belgium)