Traces of life are nearly ubiquitous on Earth. However, a central unresolved question is whether these traces always indicate an active microbial community or whether, in extreme environments, such as hyperarid deserts, they instead reflect just dormant or dead cells. Although microbial biomass and diversity decrease with increasing aridity in the Atacama Desert, we provide multiple lines of evidence for the presence of an at times metabolically active, microbial community in one of the driest places on Earth. We base this observation on four major lines of evidence: (i) a physico-chemical characterization of the soil habitability after an exceptional rain event, (ii) identified biomolecules indicative of potentially active cells [e.g., presence of ATP, phospholipid fatty acids (PLFAs), metabolites, and enzymatic activity], (iii) measurements of in situ replication rates of genomes of uncultivated bacteria reconstructed from selected samples, and (iv) microbial community patterns specific to soil parameters and depths. We infer that the microbial populations have undergone selection and adaptation in response to their specific soil microenvironment and in particular to the degree of aridity. Collectively, our results highlight that even the hyperarid Atacama Desert can provide a habitable environment for microorganisms that allows them to become metabolically active following an episodic increase in moisture and that once it decreases, so does the activity of the microbiota. These results have implications for the prospect of life on other planets such as Mars, which has transitioned from an earlier wetter environment to today’s extreme hyperaridity. Significance It 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.

Results obtained during the International Polar Year (IPY) on the thermal state of permafrost and the active layer in the Antarctic are presented, forming part of ANTPAS (‘Antarctic Permafrost and Soils’), which was one of the key projects developed by the International Permafrost Association and the Scientific Committee for Antarctic Research for the IPY. The number of boreholes for permafrost and active‐layer monitoring was increased from 21 to 73 during the IPY, while CALM‐S sites to monitor the active layer were increased from 18 to 28. Permafrost temperatures during the IPY were slightly below 0°C in the South Shetlands near sea‐level, showing that this area is near the climatic boundary of permafrost and has the highest sensitivity to climate change in the region. Permafrost temperatures were much lower in continental Antarctica: from the coast to the interior and with increasing elevation they ranged between −13.3°C and −18.6°C in Northern Victoria Land, from −17.4°C to −22.5°C in the McMurdo Dry Valleys, and down to −23.6°C at high elevation on Mount Fleming (Ross Island). Other monitored regions in continental Antarctica also showed cold permafrost: Queen Maud Land exhibited values down to −17.8°C on nunataks, while in Novolazarevskaya (Schirmacher Oasis) at 80 m a.s.l. the permafrost temperature was −8.3°C. The coastal stations of Molodeznaya at Enderby Land showed permafrost temperatures of −9.8°C, Larsemann Hills – Progress Station in the Vestfold Hills region – recorded −8.5°C, and Russkaya in Marie Byrd Land, −10.4°C. This snapshot obtained during the IPY shows that the range of ground temperatures in the Antarctic is greater than in the Arctic. Copyright © 2010 John Wiley & Sons, Ltd.

Microbes in thawing permafrost: the unknown variable in the climate change equation