The Atacama Desert, located primarily in northern Chile on the Pacific coast of South America, is recognized as one of the planet’s most extreme environments. Its reputation stems from a unique combination of geographic and climatic factors that have created a landscape of unparalleled extremity. The Atacama’s distinct features, from its profound aridity to its specialized ecosystems, make it a natural laboratory for scientists and a window to the cosmos for astronomers.
The World’s Driest Non-Polar Desert
The Atacama Desert holds the classification as the driest non-polar desert on Earth. This extreme dryness is quantified by the Aridity Index, where the core falls below the 0.05 threshold. The average annual precipitation in this central zone is less than one millimeter per year at some weather stations. The historical record illustrates the intensity of this drought, with some areas, such as the port city of Arica, experiencing periods of decades without measurable rainfall. Evidence suggests the central sector may not have received significant precipitation between 1570 and 1971.
Hosting Life in Mars-Like Conditions
The Atacama’s hyper-arid core is frequently used as a testbed for Mars missions due to its striking resemblance to the Martian surface. Life here must contend with extreme desiccation and some of the world’s highest levels of surface ultraviolet (UV) radiation. Organisms that survive in this harsh environment are known as extremophiles.
Many microbial communities thrive in endolithic habitats, taking refuge a few millimeters beneath the surface of translucent rocks, often gypsum deposits. This “rock’s habitable architecture” shields them from intense solar radiation while allowing enough light for photosynthesis. These cyanobacteria and algae synthesize protective secondary metabolites, such as scytonemin and carotenoids, which act as natural sunscreens to prevent photo-oxidative damage.
Along the coastal strip, a unique ecosystem thrives by harvesting moisture from the sea fog, locally called the camanchaca. These “lomas” fog oases support specialized flora, including bromeliads like Tillandsia and endemic cacti. These airplants depend almost entirely on the atmospheric moisture that condenses on their leaves, highlighting the highly localized nature of life in the desert.
Earth’s Window to the Cosmos
The Atacama is the premier location for ground-based astronomical observation, primarily because of its extreme aridity and altitude. The exceptionally low atmospheric humidity is the defining factor, as water vapor absorbs the millimeter and sub-millimeter wavelengths of light used to study the cold, distant universe. Minimizing this atmospheric interference provides unparalleled clarity.
Many of the world’s most advanced telescopes are situated here, including the Atacama Large Millimeter/submillimeter Array (ALMA), built on the 5,000-meter-high Chajnantor plateau. ALMA is designed to detect the faint thermal glow of the earliest and coldest objects in the cosmos, allowing it to collect data with a precision unmatched elsewhere on the globe.
Geographic Positioning and Geological Extremes
The hyper-aridity is caused by a dual geographical influence. To the east, the towering Andes Mountains create an immense rain shadow, blocking moisture-laden air originating from the Amazon Basin. This effectively prevents precipitation from reaching the Atacama plateau.
Simultaneously, the cold, north-flowing Humboldt Current runs along the Pacific coast, cooling the overlying air and creating a persistent temperature inversion. This inversion prevents the air from rising high enough to form rain-producing clouds, stripping any remaining moisture from the western side.
These long-term arid conditions have left behind unique geological formations, such as the vast Salar de Atacama. As an endorheic basin—a closed drainage system—this salt flat has accumulated minerals over millennia. Its brines contain one of the world’s highest concentrations of lithium, which is extracted using solar evaporation ponds. Another outcome of the region’s geological activity is the El Tatio geyser field, the highest in the world at 4,320 meters above sea level. This geothermal area, heated by the underlying Altiplano–Puna Volcanic Complex, features hundreds of fumaroles and geysers typically reaching only about 75 centimeters.