Bioaltered glass. Light micrograph of volcanic glass, showing tubular tracks made by glass-dissolving microbes. This sample was obtained from rock drilled 375 metres into the oceanic crust, 4000 metres below sea level. The glass was formed by super-cooled volcanic lava. The microbes probably dissolved the glass, using organic acids, in order to obtain chemical energy. The glass may also have protected them from grazing organisms. They provide evidence that organisms can influence changes in rock composition. The microbes may also influence important global cycles of minerals. Magnification: x500 at 5x7cm size.
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