In 2011 the deepest land-living creature was discovered inside a South African gold mine. A new species of nematode worm Halicephalobus Mephisto was found 3.5km below the surface. They thrive in conditions thought to be too harsh for any creature - where previously it was thought that only single-celled bacteria survive.
The discovery has also encouraged the search for life on other planets with the possibility of more creatures surviving underground.