Microbes Thrive Three Kilometers Underground

Life is so ubiquitous on Earth that scientists have found microbes about 3,000 meters below the surface inside sedimentary rock. These organisms do not occupy open caves but microscopic cracks, holes, and pore spaces containing water and dissolved nutrients. Cut off from sunlight, they obtain energy from chemical reactions involving substances such as hydrogen, methane, sulfur and iron, and their metabolisms can run as much as one million times slower than those of surface organisms.

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