Inhabited subsurface wet smectites in the hyperarid core of the Atacama Desert as an analog for the search for life on Mars

Abstract

The modern Martian surface is unlikely to be habitable due to its extreme aridity among other environmental factors. This is the reason why the hyperarid core of the Atacama Desert has been studied as an analog for the habitability of Mars for more than 50 years. Here we report a layer enriched in smectites located just 30 cm below the surface of the hyperarid core of the Atacama. We discovered the clay-rich layer to be wet (a phenomenon never observed before in this region), keeping a high and constant relative humidity of 78% (aw 0.780), and completely isolated from the changing and extremely dry subaerial conditions characteristic of the Atacama. The smectite-rich layer is inhabited by at least 30 halophilic species of metabolically active bacteria and archaea, unveiling a previously unreported habitat for microbial life under the surface of the driest place on Earth. The discovery of a diverse microbial community in smectite-rich subsurface layers in the hyperarid core of the Atacama, and the collection of biosignatures we have identified within the clays, suggest that similar shallow clay deposits on Mars may contain biosignatures easily reachable by current rovers and landers.

Influence of Physical-Chemical Soil Parameters on Microbiota Composition and Diversity in a Deep Hyperarid Core of the Atacama Desert

“…The positional coordinates are 24 • 03 49.6 S, 69 • 52 49.8 W (Figure 1). Note that the surrounding area has also been studied by Pfeiffer et al (2018) and Azua-Bustos et al (2020). Some of our findings are in accordance with Pfeiffer et al (2018), e.g., anhydrite polygons at the surface and needle fiber calcite in the soil profile.…”

“…This study also highlighted the influence of soluble salts and mineralogy on water availability and likely microbial life in the deeper parts of the soil. More recently, Azua-Bustos et al (2020) found a diverse microbial community and biosignatures in humid smectite-rich subsurface layers in the hyperarid core of the Atacama Desert (at 30-40 cm depth), and Schulze-Makuch et al (2021) showed that hypolithically colonized rocks are microbial hotspots in this desert environment.…”

“…Considering the varying minerals detected in various soil layers of the hyperarid core, such as halite, calcite, smectite, montmorillonite, dolomite, and others (Ewing et al, 2006;Fuentes et al, 2014;Azua-Bustos et al, 2020), it can be expected that the overall physicochemical properties and the microbial communities would also differ along these various layers within a soil profile. Nevertheless, microbial life in the subsurface soil of hyperarid Yungay and its relationship to physicochemical variations in soil properties have been poorly studied thus far.…”

Microbial Hotspots in Lithic Microhabitats Inferred from DNA Fractionation and Metagenomics in the Atacama Desert

“…These hotspots are characterized by hypolithic and endolithic microorganisms, as here microbiota are protected from major stressors occurring in such desert ecosystems. Therefore, this study focuses on localities where other researchers have observed the existence of islands of habitability [ 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. However, the question remains whether these islands are only a location where improved habitable conditions exist or represent actual hotspots of microbial activity.…”

“…Observations and results from previous investigators have significantly advanced our current understanding of the composition and behavior of microbial populations in the Atacama Desert [ 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Biological soil crusts, for example, have been identified as a hotspot of microbial activity and a main driver of nutrient cycling in the less arid regions of the Atacama Desert [ 27 ].…”