CAVE BIOSIGNATURES: MINERALS, MICROBES, AND MARS

Earth's subsurface is a rich source of diverse microorganisms. Caves, fissures, microcracks, and intergrain pores provide microbial homes away from the ravages of the surface. In these subterrains, microbes metabolize, often lithify in situ, and are preserved without destruction common to surface materials or diagenesis common to buried deposits. Thus, Earth's subsurface offers one of the best possible site types to search for microbial life and characteristic lithologies that life may leave behind. The subsurface may be equally valuable for astrobiology. Where surface conditions are particularly hostile (like Mars), the subsurface may offer the ONLY access to either recognizably preserved biosignatures or extant lifeforms.

We are investigating subsurface mineral/microbial associations in a variety of chemically and physically distinct Earth caves. One of our research goals is to identify detectable macroscopic, microscopic, and chemical characteristics that are unequivocally biogenic. We have identified numerous individual cave biosignatures. However, to be especially useful for astrobiology, we are looking for suites of characteristics. Ideally, "biosignature suites" should have macroscopically and microscopically detectable features, be independently verifiable by non-morphological means, and independent as possible of specific chemistries of the responsible organisms. This is a demanding set of requirements.

Because we are working in fragile, non-renewable and frequently legally-protected environments, we are developing non-invasive and minimal impact analytical techniques for life and biosignature detection and characterization. Moreover, we are working under difficult field conditions that share many limitations common to extraterrestrial robotic and human missions. Thus, the cave/subsurface astrobiology model addresses the most important goals from both scientific and operational points of view.

We will present the details of cave biosignature suites in materials like moonmilk, Crisco, pool fingers, u-loops, snottites, and others involving minerals ranging from manganese and iron oxides to calcite. Biosignatures include morphological fossils, mineral-coated filaments, living microbial mats and preserved textures on diverse surfaces, d¹³C and d³⁴S values consistent with microbial metabolism, genetic markers, and unusual elemental abundances and ratios.