There are weather stations in the interior of Chile's Atacama Desert that have never recorded rain. Not "very little" rain — none, in the entire history of their record-keeping. The desert's average rainfall is commonly put at around a millimetre a year, and parts of its hyperarid core are believed to have gone not years but centuries without a meaningful shower. The port city of Arica, on the desert's northern edge, ranks among the driest inhabited places on Earth. When rain does fall somewhere in the Atacama, it can make national news.
The geography is a conspiracy of accidents. The Atacama runs for roughly a thousand kilometres down northern Chile, pinned between the Pacific Ocean and the Andes. To the east, the Andes form a colossal rain shadow, wringing out the moist air flowing from the Amazon basin long before it reaches the desert. To the west, the cold Humboldt Current chills the air above the ocean, so that instead of rising and forming rain clouds it slides ashore as a low, clammy fog the locals call camanchaca. A stubborn zone of high pressure over the south-eastern Pacific caps the whole system. The result is a desert beside a sea: villages have learned to harvest the fog itself, stringing up fine mesh nets that comb drinking water out of the passing mist.
The oldest desert on Earth
This is not a young dryness. Geologists believe parts of the Atacama have been arid for tens of millions of years, making it very likely the oldest desert on Earth — and its hyperarid heart is rivalled for sheer rainlessness only by the frozen McMurdo Dry Valleys of Antarctica, a favourite quizmaster's trap. The aridity preserved treasure. Sodium nitrate — Chile saltpetre, prized for fertiliser and explosives — accumulated here as nowhere else, and in the nineteenth century it made fortunes: the War of the Pacific (1879–84) was fought largely over the nitrate grounds, ending with Chile taking the desert coast and Bolivia losing its access to the sea, a grievance Bolivia nurses to this day. The abandoned nitrate towns of Humberstone and Santa Laura still stand, mummified by the dry air, as a UNESCO World Heritage site.
People, too, were preserved. The Chinchorro culture of the Atacama coast began artificially mummifying their dead roughly seven thousand years ago — some two millennia before the Egyptians — making theirs the oldest deliberate mummies known anywhere in the world.
Mars on Earth
The driest soils of all lie around Yungay, in the desert's core, and they are so hostile that scientists have struggled to find life in them at all. In a much-cited experiment, researchers ran tests like those carried out by NASA's Viking landers on Mars and got the same bleak answer: soil that looked, chemically and biologically, close to dead. That is precisely why space agencies love the place. NASA and the European Space Agency have used the Atacama for years to trial Mars rovers, drills and life-detection instruments — if a sensor can find the desert's scarce, salt-encrusted microbes here, it stands a chance on Mars. The desert's chemistry, including Mars-like perchlorate salts, completes the impression of another planet conveniently located on this one.
The same dryness makes the Atacama the best window on the universe we have. With hundreds of cloudless nights a year and almost no water vapour overhead, its high plateaus bristle with observatories: the ALMA radio telescope array sits on the Chajnantor plateau at around five thousand metres, while the Very Large Telescope peers out from Cerro Paranal.
And yet the desert is not quite dead. Microbes shelter inside salt crusts and under translucent stones. In rare years when rain reaches its southern fringes, dormant seeds detonate into the desierto florido — a sudden carpet of blooms across land that looked lifeless. The Atacama also staged one of the century's great survival stories: in 2010, thirty-three miners were trapped nearly seven hundred metres underground at the San José mine near Copiapó and rescued, all alive, after sixty-nine days. Beneath the desert lie other riches — Chile's vast copper mines and, in the brine of the Salar de Atacama, one of the world's great stores of lithium.
The Atacama is what remains when water is subtracted from the world: salt, silence, starlight — and just enough life to teach us how to search for it on another planet.
Quiz nuggets
- Some weather stations in the Atacama Desert have never recorded rainfall; average precipitation is around a millimetre a year.
- The Atacama is widely considered the world's oldest desert, its driest rival being Antarctica's McMurdo Dry Valleys.
- NASA and ESA test Mars rovers and life-detection instruments in the Atacama because its Yungay soils are nearly lifeless, like Martian ground.
- The Chinchorro people of the Atacama coast made the world's oldest artificial mummies, about two thousand years before Egypt.
- The War of the Pacific (1879–84) over Atacama nitrates cost Bolivia its coastline; the ALMA observatory now sits at about 5,000 metres on the Chajnantor plateau.