Bacteria survive inside salt crystals in the driest desert, extracting water from morning dew absorbed by hygroscopic salts. They represent the minimum water requirement for life on Earth.
The driest life on Earth
In the Salar de Atacama, the driest non-polar desert on Earth, life exists where it was once thought impossible. The surface of this vast salt flat appears sterile, receiving less than two millimeters of precipitation annually. Yet, hidden just millimeters beneath the surface of translucent halite (rock salt) crystals, entire microbial communities thrive. These organisms are endoliths—creatures that live inside rocks. This habitat contains a mix of cyanobacteria, archaea, and other bacteria that have adapted to an existence defined by extreme dryness and intense solar radiation.
Their survival depends on the salt itself. Halite is hygroscopic, meaning it naturally absorbs atmospheric moisture. Each morning, as marine fog rolls in and relative humidity briefly rises above 75%, the salt crystals pull enough water vapor from the air to create microscopic films of liquid brine within their structure. This process, deliquescence, provides the water necessary for the endolithic community to activate its metabolism for a short time. The salt crystal also shields, filtering out the harsh ultraviolet radiation that bombards the desert surface, while allowing just enough light (about 0.02% of incident PAR) to penetrate for photosynthesis.
Pushing the limits of biology
The organisms within the Atacama's salt crusts represent life at its absolute water limit. They exist in a state of near-constant desiccation, only becoming metabolically active when deliquescence provides temporary brine. Studies have documented diverse communities, including cyanobacteria of the genus Halothece and various salt-loving archaea from the class Halobacteriales. These communities cycle carbon on timescales ranging from years to decades, depending on the scarce availability of water.
This remarkable survival strategy has significant implications for astrobiology. The Atacama Desert is a the most important Mars analog environments on Earth because of its extreme aridity and soil chemistry. Scientists use this natural laboratory to test life-detection instruments and drilling technologies for future missions to Mars. The discovery that life can persist within salt crystals by drawing water from the air shows that if life ever existed on Mars, its biosignatures might be preserved in similar evaporite deposits. NASA's Atacama Rover Astrobiology Drilling Studies (ARADS) project specifically investigates these environments to refine strategies for searching for life on other planets.
💡Fun Facts
Some of the microbes found here belong to the genus *Chroococcidiopsis*, a type of cyanobacteria known for its extreme resistance to radiation and dehydration.
The salt crusts were long considered sterile until the discovery of these endolithic communities.
While the microbes are protected from UV rays, the translucent halite allows enough light for photosynthesis, the process that provides the primary energy for this unique ecosystem.
Scientists have found microbes living up to two meters below the desert surface in hypersaline soils rich in halite.
The Salar de Atacama is part of the Los Flamencos National Reserve, which has specific access points like the Chaxa Lagoon with visiting hours, typically from 8:00 AM to 4:00 PM. Independent access to the wider salt flat is generally unrestricted.
Admission
Entry to specific sectors like Laguna Chaxa requires a fee, payable at the entrance.
Accessibility
The terrain is flat but can be uneven and sharp. It is fully exposed to the sun with no shade. Sturdy footwear and sun protection are essential.