Presentation #403.08 in the session Into the Unknown: Astrobiology and Habitability.
Micro-tubular and granular dissolution textures containing biomolecules and other chemical evidence of life have been found in sideromelane glasses from seafloor basalts. These putative biosignatures are hypothesized to form when lithotrophic microbes dissolve glass as they metabolize redox-sensitive elements such as Fe, S, and Mn. Recently, such biosignatures have been documented in terrestrial settings, including tuffs and hyaloclastite breccias from mafic phreatomagmatic eruptions.
The Fort Rock Volcanic Field (FRVF) in Oregon, USA, is a volcanic field which erupted from the late Pliocene – late Pleistocene into paleo-Fort Rock Lake, producing tuff cones, tuff rings, and maar craters. Lavas are olivine-tholeiite basalts, and tuff samples have been partially altered to palagonite. Alteration minerals indicate saline, alkaline lake fluids. A similar, slightly older volcanic field is the Western Snake River Plain (WSRP) of Idaho, USA. At WSRP, olivine-tholeiite basalts erupted into paleo-Lake Idaho during the Pliocene and early Pleistocene, creating maars, tuff cones, tuff rings, and hyaloclastic pillow lavas, depending on lake levels.
We have found biogenic alteration in tuff samples collected in 2010 from FRVF. Granular alteration is common in most glass clasts that have undergone some palagonitization. Curvilinear tubules with some branching or budding features averaging 5-20 um in length and 1-2 um diameter — consistent with the sizes of bacteria and archaea — were identified in several samples. In 2022, we collected samples from WSRP. We will complete the same analyses on both sample suites, including petrography, X-Ray diffractometry, X-Ray fluoresence spectroscopy, and electron micro-probe analysis. WSRP samples will be compared geochemically and mineralogically to FRVF samples to document consistent geological properties correlated with biosignatures.
The FRVF and WSRP environments are analogous to Gusev Crater on Mars, where in situ measurements from NASA’s Spirit rover showed a mafic hydrovolcanic environment with subsequent periods of high- and low-temperature alteration. Further, amorphous glass is wide-spread on the surface of Mars, potentially providing a habitat to lithotrophs during periods of water-rock interactions. Our findings from FRVF suggest that these Mars-relevant environments are habitable for microbes, and we hope to expand the record of biosignatures in glasses with our WSRP samples. The geological properties that are associated with biosignatures in multiple localities can be used as exploration targets when searching for biosignatures on Mars.