CARBONATE SHRUBS IN TRAVERTINES OF TIVOLI, ITALY: CAN MORPHOLOGY BE USED TO DISTINGUISH BETWEEN BIOTIC AND ABIOTIC PRECIPITATES?
In this study, shrubs similar in morphology to those observed in natural travertines were precipitated abiotically from a solution of oxalic acid dihydrate and acetone. Photomicrographs of the precipitates and bacterial colonies from Ben-Jacob (1997) were compared using a model that parameterizes morphology via link-length ratio (R1), bifurcation angle (β), and branching ratio (RB) (Cheetham et al. 1980). Whereas R1 and β were unsuccessful in separating biotic from abiotic shrubs, RB proved consistent in making this distinction. Data were used to establish fields of biogenicity and abiogenecity within the range of shrub morphospace, and the model was then applied to travertine shrubs from Italy. Natural travertine shrubs plotted entirely within the field of abiotic precipitates. These preliminary data suggest that travertine shrubs from Italy are abiogenic, and that morphometric classification may be an effective method of approaching questions of biogenicity, especially in Martian deposits where the only data available may be morphological in nature. The model will be refined by applying kernel density and cluster analyses to establish a confidence interval for biogenicity.