Rock-eating bacteria. The bacteria (red) revealed in this colour fluorescence micrograph are the first known forms of life on Earth that do not ultimately depend on energy from sunlight. They were found in 1995 in pools of water sandwiched between layers of solid rock over 1000m below the Earth's surface. Deprived of organic matter, light and oxygen, they are thought to obtain energy from hydrogen in rock (green) and carbon from dissolved carbon dioxide. Their discovery hints at what life may have been like before the evolution of photosynthesis and indicates a potential for life on Mars. Magnification: x550 at 6x4.5cm size. x800 at 4x5"~PORTRAIT"