BIOGEOPHYSICS: A NEW FRONTIER IN EARTH SCIENCE RESEARCH

Biogeophysics'' is a rapidly evolving Earth science discipline concerned with the geophysical signatures of microbial interactions with geologic media. It spans the established disciplines of geomicrobiology, biogeoscience, and geophysics. Biogeophysics research in the last decade has confirmed the potential for geophysical techniques to measure not simply the physical and chemical properties of the subsurface, as already well established, but also to detect microbes, microbial growth, and microbe-mineral interactions, thus representing a major paradigm shift in geophysical thinking. In this review we begin by defining biogeophysics and provide a historical perspective. We then consider microbial alterations of petrophysical properties as such alteration is the source of most biogeophysical signals. Our review then focuses on geophysical interrogation of microbial processes, including the direct detection of microbial cells and biofilm formation, microbial metabolic by-products, microbe-mediated redox processes, and biogeochemical and microbe-mineral transformations. We conclude by discussing challenges, opportunities, and potential new applications of biogeophysics to the exploration of life in extreme environments, e.g., the deep biosphere, the cryosphere, and other planets. We find that published biogeophysics studies to date are mostly observation based, presenting only empirical relationships between microbial and geophysical variables. Future research endeavors must focus on developing theoretical and/or numerical models for predicting geophysical signals arising from microbial activity.