Abstract
Abstract. The hyperarid core of the Atacama Desert, Chile, is possibly the driest and most life-limited place on Earth, yet endolithic microorganisms thrive inside halite pinnacles that are part of ancient salt flats. The existence of this microbial community in an environment that excludes any other life forms suggests biological adaptation to high salinity and desiccation stress, and indicates an alternative source of water for life other than rainfall, fog or dew. Here, we show that halite endoliths obtain liquid water through spontaneous capillary condensation at relative humidity (RH) much lower than the deliquescence RH of NaCl. We describe how this condensation could occur inside nano-pores smaller than 100 nm, in a newly characterized halite phase that is intimately associated with the endolithic aggregates. This nano-porous phase helps retain liquid water for long periods of time by preventing its evaporation even in conditions of utmost dryness. Our results explain how life has colonized and adapted to one of the most extreme environments on our planet, expanding the water activity envelope for life on Earth, and broadening the spectrum of possible habitats for life beyond our planet.
Highlights
Water is the single most important requirement for life on Earth
The layering and characteristic pore size distribution of the pinnacles are the result of small-scale water dynamics in the natural environment, and at the same time the small pores likely affect the way in which water is exchanged between the interior of the halite and the atmosphere, which controls the colonization
We propose that the small pore spaces within these phases correspond to the smallest porosity measured by mercury intrusion porosimetry, and are responsible for the occurrence of liquid water at relative humidity (RH) < deliquescence relative humidity (DRH) indicated by our microclimate data
Summary
While specialized organisms can exist in all but the most arid parts of the Earth, at some point water is too scarce to permit the full range of functions necessary to sustain viable populations of organisms, and biological adaptation to desiccation is no longer possible We call this threshold the dry limit of life. A second strategy, exemplified by most lichens and some cyanobacteria, is to supplement liquid water from air humidity (Lange et al, 1994; Palmer and Friedmann, 1990a, b) These strategies have worked successfully in all hot and cold deserts on Earth, except in some parts of the Atacama Desert, in Chile, which appear to be too dry even for these strategies to be effective
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