Real-time 3D light microscopy provides a large depth of field and high resolution which have considerable advantages for the discovery and examination of microbial structures in rocks. In highly translucent specimens, real-time 3D observation in transmitted light offers a greater capability for rapid recognition of microbial features than do other 3D imaging methods such as light microscopy of serial sections or tilted specimens, scanning electron microscopy, stereology, confocal microscopy, or computed tomography. Application of this new technique to samples of Precambrian, Permian, Cretaceous, and Pleistocene age reveals an intriguing variety of probable microbial structures, particularly in sparry calcites. A direct view of the true spatial relationships among microbial structures and between microbial structures and mineral substrates provides essential clues for deciphering the controls on and timing of microbial activity relative to chemical and mechanical processes in rocks.

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