The Viking missions showed the martian soil to be lifeless and depleted in organic material and indicated the presence of one or more reactive oxidants. Here we report the presence of Mars-like soils in the extreme arid region of the Atacama Desert. Samples from this region had organic species only at trace levels and extremely low levels of culturable bacteria. Two samples from the extreme arid region were tested for DNA and none was recovered. Incubation experiments, patterned after the Viking labeled-release experiment but with separate biological and nonbiological isomers, show active decomposition of organic species in these soils by nonbiological processes.

SignificanceIt has remained an unresolved question whether microorganisms recovered from the most arid environments on Earth are thriving under such extreme conditions or are just dead or dying vestiges of viable cells fortuitously deposited by atmospheric processes. Based on multiple lines of evidence, we show that indigenous microbial communities are present and temporally active even in the hyperarid soils of the Atacama Desert (Chile). Following extremely rare precipitation events in the driest parts of this desert, where rainfall often occurs only once per decade, we were able to detect episodic incidences of biological activity. Our findings expand the range of hyperarid environments temporarily habitable for terrestrial life, which by extension also applies to other planetary bodies like Mars.

[1] Fog is the most important source of water for native plants and biological soil crusts in the Atacama Desert. Since fog depends upon available moisture, an understanding of climatic patterns is essential to interpret its present-day occurrence and distribution. In this work, temperature and humidity of ambient air and collected fog water in selected sites were studied across a transect from the coast to inland of the Atacama Desert, by using automated outdoor sensors for temperature and relative humidity, and also fog collectors equipped with automated rain gauges to measure collected fog water flow rates. Field measurements were organized to determine fog and collected fog water patterns at three selected sites, namely, Coloso, Inacesa and Yungay in addition to the relative humidity and temperature variation with altitude at Coloso Mountain located within Coloso site. The results show a decreasing trend in the collected fog water flow rates from the coast toward inland locations. Daily thermal oscillations at each site are closely related to fog water collection. At Coloso Mountain, an adiabatic cooling-like effect of the wind ascending its slope was observed preferentially during nighttime. At daytime, occasional distortions observed in the temperature profiles are probably produced by a thermal driven-air convection process along the Coloso Mountain slope heated by solar radiation. The reduction in available water from fog from the coast to the inland site is consistent with the reduction in colonization rate for hypolithic cyanobacteria along this same transect.Citation: Cáceres, L., B. Gómez-Silva, X. Garró, V. Rodríguez, V. Monardes, and C. P. McKay (2007), Relative humidity patterns and fog water precipitation in the Atacama Desert and biological implications,

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The arid conditions in northern Chile restrict the access to water and energy and the development for small mining entrepreneurs. For this purpose, this work describes the experimental behavior of a novel sustainable solar water heating system that is suitable for open ponds combined with floating covers and photovoltaic cells which supply the required energy for water pumping and measurement accessories. The heating is provided through solar panels and coil heat exchanger;

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