Devil worm discovered deep in Earth's crust

A tiny worm, Halicephalobus mephisto, found 0.8 miles (1.3 km) underground in a South African gold mine, is the deepest-living animal ever discovered. The 2011 discovery challenged assumptions that complex life could not survive without sunlight or oxygen. Researchers have since studied its descendants to understand how it thrives in hot, dark conditions, expanding the limits of known life.