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Project Progress

We have studied the nano-structured calcite in modern and ancient soils (paleosols) and compared them to minerals synthesized using controlled organic components. Both modern soils and paleosols of eolian sediments (loess) that formed in arid and semi-arid environments will provide useful information about possible bacterial activities on Mars. Results from both SEM and TEM investigations show that nano-fibrous calcite in semi-arid soils of loess sediments is common. These calcite nano-fibers have unusual elogation directions in well crystallized single crystals that have smooth edges. Such kinds of calcite cannot be produced in a purely inorganic system. We suggest that bioorganics derived from microorganism controlled the growth of the nano-fibrous calcite in dry soil environment.

We also investigated a basalt vent deposit from Snake River Plain of Idaho using X-ray diffraction and transmission electron microscopy. The layered pyroclastic and volcaniclastic vent materials (basaltic glass) was produced by phreatomagmatic eruptions in the late Miocene to early Pliocene. The maghemite nano-crystals in the samples are closely associated with Fe-bearing smectite and a zeolite of phillipsite. TEM images also show maghemite nano-fibers (arrays of nano-crystals) of maghemite with an average diameter of ~ 6 nm, in close association with smectite. The Ti-free maghemite nano-crystals and nano-fibers are interpreted to have transformed from precursor magnetite nano-crystals through topotactic oxidation. The precursor magnetite nano-crystals were products of dissimilatory iron reduction of ferrihydrite nano-crystals through topotactic transformation under anaerobic conditions. Magnetite / maghemite nano-fibers are interpreted to have formed by microbial activity through oriented attachment of magnetite nano-crystals, providing evidence that such features may serve as a biosignature.