See more from this Division: Topical Sessions
See more from this Session: Microbialites: A 3.5-Billion-Year Record of Microbe-Sediment Interactions
Abstract:
Here, we compare/contrast two different stromatolites as a cautionary tale for exobiologic studies. The stromatolites are basically identical at the hand sample scale (e.g., the scale most easily imaged by a rover). Both are small (~15 cm tall) branching columnar structures that display finely laminated light-dark lamination on the order of ~100 microns thick. The laminae tend to thicken over the tops of the columns and thin towards the sides.
Microscopic examination reveals the laminae in one stromatolite, collected from a subsidiary pool to Obsidian Hot Spring in Yellowstone National Park, are composed entirely of silicified microbial filamentsa classic biogenic structure, with an active cyanobacterial mat on the surface. The laminae in the other stromatolite, collected from a hydrothermal vein in the Tempaiute Range, Nevada, are composed of interlocking bladed calcitea classic abiotic precipitated fabric. Furthermore, the Tempaiute stromatolites grew surface normal to a high-angle hydrothermal vein deep in the subsurface, in the absence of light.
While the geologic context provides some hint to their potential biogenicity (hot spring/active mat versus subsurface vein), the context may not always be apparent (e.g., a Mars boulder field). At the hand sample scale, many stromatolites may fail the extraordinary evidence testif possible, such structures should be examined in-situ microscopically to help guide our decision.
See more from this Division: Topical Sessions
See more from this Session: Microbialites: A 3.5-Billion-Year Record of Microbe-Sediment Interactions