Rock-eating SLIME bacteria. Coloured confocal laser scanning micrograph of a microcolony of unidentified SLIME bacteria found deep in rocks underground. Bacterial cells are red, basalt rock is green, with yellow filamentous-shaped minerals (at centre) formed at the surface of the colony. These bacteria are called SLIME's (subsurface lithoautotrophic microbial ecosystems). They were found in 1995 sandwiched between layers of solid rock 1000m below the Earth's surface. Deprived of light and oxygen, they may be methanogens feeding on hydrogen in rock and dissolved carbon dioxide. They may be Archaea (a primitive bacteria group).