Thesis Format

Integrated Article

Preservation of Putative Biosignatures in Terrestrial Mars-relevant Hydrovolcanic Environments

Author

Catheryn H. Ryan, Western UniversityFollow

Degree

Doctor of Philosophy

Program

Geology

Collaborative Specialization

Planetary Science and Exploration

Supervisor

Schmidt, Mariek E.

Affiliation

Brock University

2nd Supervisor

Osinski, Gordon R.

Co-Supervisor

Abstract

Hydrovolcanic tuff deposits contain abundant, hydrothermally-altered glass and act as a habitable niche for microorganisms. Similar environments identified on Mars are considered potential targets for astrobiological investigation. Tuffs sometimes contain evidence of possible microbially-mediated alteration, including microtubules (~1 µm diameter and ~10 – 20 µm length) and granular alteration in glass. These microscopic textures are considered putative biosignatures based upon their morphology, size distribution, and geochemical characteristics.

In this thesis, a database of volcanic fields with characteristics relevant to Mars and with potential to preserve putative biosignatures in glass is presented. The database contains 45 volcanic fields distributed globally. At seven sites, there is published evidence of microbial biosignatures in the glass. The remaining volcanic fields were compared to these biosignature-bearing sites and Martian volcanic rocks and 11 are recommended as high-priority targets for future investigation.

Two sites were explored in-depth. We present the first report of putative biogenic alteration in glass from the Pliocene-Pleistocene hydrovolcanoes of Western Snake River Plain, Idaho, USA. New biosignatures from the Fort Rock Volcanic Field, Oregon, USA are also provided. Samples collected from tuffs erupted into paleo-Lake Idaho and paleo-Fort Rock lake have glass which has partially altered to palagonite, a low-temperature alteration product. Some samples contain microtubules and granular alteration in the glass. Optical microscopy and µXRD were used to determine the textural relationships between fresh glass, glass containing microtubules, palagonite, and other alteration minerals in void spaces (calcite, zeolites). These textural relationships indicate that tubules formed under low-temperature hydrothermal conditions during palagonitization, amidst alteration mineral precipitation. Geochemical measurements and element mapping with an electron microprobe were used to compare samples with and without biosignatures, and compare volcanic fields to each other. We found little distinction in composition between microtubule-bearing and non-microtubule-bearing glasses at either volcanic field. Microtubules were more abundant and morphologically diverse in Fort Rock samples. Differences in paleo-lake evolution and glass and fluid chemistry between the sites may account for this variation, with favourable conditions for biosignature preservation at Fort Rock. Both volcanic fields have geochemical, mineralogical, and environmental properties relevant to Mars, and represent testing grounds for future astrobiological missions.

Summary for Lay Audience

When hot magma and water interact, an explosive volcanic eruption occurs that produces volcanic glass. These glass-rich volcanic deposits are called tuffs. Tuffs will react with water and produce new minerals, such as palagonite, clays, and zeolites. This alteration process can provide an energy source for microbes. Microbes may create micro-textures in the glass as they interact with it. Micro-textures are a potential record of life, also known as a biosignature. Biosignatures have been found in tuffs from many places around the world. They could potentially be found in similar environments on Mars.

I have created a list of 45 volcanic fields on Earth with similarities to Mars that could potentially preserve biosignatures. Seven of the volcanic fields already have reports of these biosignatures. I compared the remaining sites to these seven fields and to data from Martian rocks. I created a ranked list of sites where biosignatures can be preserved in a Mars-like setting.

I then explored two of these volcanic fields in-depth: The Western Snake River Plain volcanic field in Idaho, USA and the Fort Rock Volcanic Field in Oregon, USA. These volcanic fields are similar. Both contain volcanic structures which erupted into lakes. The volcanoes have a similar chemical composition, and the tuffs from these volcanoes were altered when they reacted with water. Both volcanic fields have properties that are akin to Mars. I report here the first evidence of biosignatures in tuffs from the Western Snake River Plain. I also expand the record of biosignatures in tuffs from Fort Rock. I compared minerals and geochemistry between rocks that have biosignatures and rocks that do not at both volcanic fields. I found little to distinguish rocks with biosignatures from rocks without biosignatures. Fort Rock Volcanic Field had more widely-distributed and diverse biosignatures in its tuffs. There may have been better conditions for forming and preserving biosignatures at Fort Rock. This work is important for our understanding of how biosignatures are formed and preserved, and for investigations of potential life on Mars.

Recommended Citation

Ryan, Catheryn H., "Preservation of Putative Biosignatures in Terrestrial Mars-relevant Hydrovolcanic Environments" (2024). Electronic Thesis and Dissertation Repository. 10508.
https://ir.lib.uwo.ca/etd/10508

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.