Microorganisms inhabit almost every conceivable environment on the planet’s surface, and extent the biosphere to depths of several kilometers into the crust. Significantly, the chemical reactivity and metabolic diversity displayed by microbial communities make them integral components of global elemental cycles, from mineral dissolution and precipitation reactions, to aqueous reduction-oxidation processes. In that regard, microorganisms have helped shape our planet overthe past 4 billion years and made it habitable for higher forms of life. In this course we will evaluate the geological consequences of microbial activities, by taking am interdisciplinary and “global” view of microbe-environment interactions.