OBSERVATIONS OF EXPERIMENTAL MICROBIAL ETCH TEXTURES OF OLIVINE: A POTENTIAL BIOSIGNATURE?

We are continuing the investigation of the textural effects of microbial etching on olivine surfaces (Longazo et. al, GSA 2000). The goal is to determine whether such features could serve as a biosignature in silicates. Three series of experimental trials have been conducted using both biotic and abiotic conditions to characterize the textural changes on olivine surfaces. The most large-scale changes observed are preferential surface etching/dissolution features. Typical features consist of either etch-pits or channels aligned along a specific crystallographic axis of the olivine, most likely along the (001) axis. Microbial colonies preferentially align themselves along the edges of the larger etch structures (> 1 ìm). The presence of nanometer-sized (<100nm) etched imprints (nanoetching) mimics the outlines of the biofilms associated with the microorganisms and occur along on these same edges. Nanoetch-like features are distinctly not abundant in the abiotic experiments, nor are they morphologically similar to the biotic experiments; this suggests the presence of nanoetching is uniquely associated with the colonization of microorganisms on a silicate substrate. However, qualitative morphology alone is not a strong biosignature. We suggest that, with further statistical analyses, these nanoetching features could serve as a potential biosignature for microbial activity. Future work will repeat experiments and the olivine will be microtomed and examined by TEM. The goals are to investigate the preferential alignment of the microbes along crystallographic axes, and the interaction between biofilm and the silicate substrate. We will also investigate vertical profiles of the etch/dissolution surfaces using white light scanning interferometry.