The Atacama Desert is a vast region spread across an area of about 105,000 square kilometers. One of the most hyperdry zones in the world, there are regions in the Atacama with annual average precipitation of only 15 millimeters per year, others with just 1–3 millimeters per year, and some spots where rain hasn’t fallen in decades.
One of the driest areas of the Atacama is the Yungay Valley in northern Chile. Here, a team led by Lucas Horstmann, a Ph.D. student at the GFZ German Research Centre for Geosciences in Potsdam, Germany, and Dirk Wagner, a geomicrobiologist there, carried out excavations in search of life in the subsoil.
Previous investigations had been conducted in the same area, but Wagner and Horstmann dug deeper—literally. While earlier research found microbes at depths of about a meter, the new study documented rich, previously unknown bacterial communities at depths of 4 meters. The researchers published their findings in the Proceedings of the National Academy of Sciences Nexus.
The deep discovery has implications beyond the Atacama. As Alida Pérez-Fodich, a geochemist at the University of Chile who was not involved in the study, explained, “This research shows that it is possible to find life not only on the surface of deserts, but also on deeper levels under the soil, and to recognize the taxon of these living microorganisms. This is an important finding of the research: not only to say that there is life beneath the dry soil, but also to say who these inhabitants are.”
Life on the Fringe
The microorganisms analyzed by the team came from the phylum actinobacteriota, which are often found in arid and pristine soils. Researchers said that actinobacteria communities colonized the Atacama’s alluvial fans approximately 19,000 years ago.
“Climate has been stable for thousands of years, always desertic, but with differences between arid and semiarid soils,” Wagner said.
“These organisms,” explained Linda Daniele, an expert in hydrogeochemistry at the University of Chile who was not involved in the research, “have developed methods of survival outside of the conventional ways, staying more on the fringes of all that we consider nutrients and elements essential for life.”
To explain the bacteria’s life on the fringes, Horstmann and his coauthors proposed that the organisms rely on water generated by the mineralogical change from gypsum to anhydrite. “This change indeed leaves some amount of water in the environment,” Daniele said, “and this water could be used by the bacteria.”
“Vesicular gypsum is pretty common in the Atacama Desert,” Horstmann said. “Sulfates that originate from the Pacific Ocean and are transported inland via fog precipitate in the soil. Due to the dryness and limited rain events, there’s no dissolution of the salt, and that’s when they accumulate in the surface soils. This [accumulation] creates a gypsum plaster near the surface.”
Martian Proxy
In addition to a better understanding of how microbial communities function in subsurface soils, the new research may also help the search for extraterrestrial life.
“In general,” Wagner explained, “every study that has been conducted about Mars has been focused on the surface of the Atacama Desert. To be able to study what happens under the subsurface, then, offers a bigger potential to study life on Mars. To understand the deep biosphere in the Atacama Desert could help a lot to understand what life on Mars could potentially be like.”
—Alejandro Pardo, Science Writer
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