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Project Progress

We have characterized mineralogical biosignatures that consist primarily of iron oxyhydroxide minerals formed as the result of microbial activity in near-neutral pH solutions. This work has employed biological sample preparation for electron micoscope characterization, and analysis via transmission electron microscopy. Work has focused on determination of the phase, particle size, morphology, microstructure, and role of polymeric compounds in templating nucleation and growth. We have established that bacteria can grow by utilizing ferrous iron released by iron silicate mineral dissolution, examined the relationships between dissolution kinetics and morphology, identified polymer biosignatures in which pseudo-single crystals of “metastable” phases adopt extraordinarily large (~1000:1) aspect ratios as the result of polymer-directed nucleation, and characterized products of crystal growth during aging of some biomineral-polymer aggregates. Samples have been examined from terrestrial and oceanic habitats. Results indicate considerable diversity in polymer-aggregate structure and mineralogy. However, it is likely that all neutral pH biological oxide mineral precipitation processes take advantage of the proton gradient developed following iron oxide deposition. We have conducted experiments to investigate the details of polymer fibril mineralization and have been able to simulate the structural and morphology controls documented in the natural examples. We have established that crystal growth by oriented aggregation is a key mechanism in iron oxide nanoparticles, leading to distinctive dislocation and twin microstructures. In parallel, we have conducted a detailed study of sulfide mineral biosignatures that form in anaerobic zones and established the importance of << 2 nm diameter particles in Zn-S chemistry.