Project 3

The Curiosity rover has been investigating an unequivocally habitable environment in Gale crater, interpreted as a shallowing lacustrine environment with localized areas of hydrothermal alteration, post-depositional fracturing and fluid mineralization, and subaerial desiccation. This environment hosts a wide array of subaqueous and subaerial environments that preserve evidence for both inundation and desiccation, suggesting the presence of localized microhabitats within the broader habitable lacustrine-dominated environment. Comparable Precambrian sedimentary environments on Earth have been shown to preserve fossilized evidence of widespread microbial mats and “biocrusts” within the geologic record (e.g., Beraldi-Campesi et al., 2014). If fossilized evidence for comparable microbial communities are preserved within the Martian geologic record at the Curiosity rover exploration zone, would the rover be able to definitively detect them? Although preserving the morphological signatures of ancient biocrusts in the Martian geologic record might be possible, Curiosity carries more capable geochemical instruments than geologic hand tools capable of excavation. Therefore, we propose approaching this question through a detailed geochemical investigation of how biocrusts “spatio-chemically” organize the landscape, especially over variable topography like mudcracks or ridges. We hypothesize that the Curiosity rover has recorded definitive spatio-chemical evidence for biocrusts at the Gale crater exploration zone. To test this hypothesis, we must: (1) Derive key spatio-chemical markers of modern terrestrial biocrusts during their development under variable field settings and controlled greenhouse conditions [using guided machine learning techniques]; (2) Confirm that these spatio-chemical markers of modern biocrusts are still preserved in the fossilized Precambrian biocrusts found throughout the southwestern United States; and (3) Conduct an investigation of Martian bedrock surfaces throughout Gale crater using measurements from the ChemCam and APXS instruments to look for comparable spatio-chemical trends.

We will be using the Tracer5i, which is a portable X-ray fluorescence spectrometer (pXRF) to predict and identify the flow of nutrients and elements across different parts of our inoculated biocrusts. The pXRF has been used to assess the concentration of macro- and micronutrients of organic surfaces like plants (Viera da Costa, et al. 2013). Elements that we will be assessing with the pXRF are bio important elements such as nutrients like phosphorus, potassium, calcium, and magnesium. We will be comparing this to non-bio important elements such as aluminum or titanium. The pXRF, when pressed against the solid surface of our object of interest, shoots an x-ray to excite its atoms to release electrons that will tell us more about its elemental makeup. We will be using R and the caret package to create estimation models. Our collection of large data sets from our trials of inoculation and growth will be inputted in a developing machine learning model. These models can be applied to both nutrient flow across biocrust and help identify biocrust structures. Greenhouse Materials Our inoculant will be a mixed cyanobacterial community with some lichens mixed in sourced from the Sonoran Desert (McDowell-Sonoran Preserve). We will be distributing this methodically across different bins of sand to test different growing conditions. Our substrate will be commercially available Play Sand. We will be using plastic bins to hold our substrate and create depressions with the bottoms of ice cube trays. Prior to addition of the biocrust, we will artificially create patterns in the sandy surface to generate differences in microtopography, and in key growth factors such as light, temperature and moisture retention. Using an ice cube tray, we will press it against the top of the soil to create different topography to create indentations, or cracks on the soil. We will also use the tray upside down to create small mounds. We estimate that our biocrust will grow over
this surface for about 2 ½ months, and we will monitor growth multiple times per week. We will apply supplemental fertilizer to supply relevant biological elements. Our fertilizer is called Knop’s solution, which is a mix of macro and micronutrients and Aluminum Sulfate. Aluminum sulfate salt is the only element that we will be adding. This will ensure a homogeneous layer of a non-bio important element (aluminum) that the biocrust would not be assumed to move. The fertilizer will be applied once every 2-3 weeks to our bins with a spray bottle. The designated area will be sprayed to potentially see if the fertilizer will affect not only the growth of the biocrust but also its elemental makeup.

The student will present the results of the work at the NASA Space science conference and ideally publish in the results of the work in JGR
biogeosciences.