A look at the driest place on Earth, the Atacama Desert in South America which is 50 times dryer than Death Valley; and how even in such a barren place, bacteria can still thrive. The Atacama Desert (Spanish: Desierto de Atacama) is a plateau in South America, covering a 1,000-kilometre (600 mi) strip of land on the Pacific coast, west of the Andes mountains. It is the driest hot desert in the world. The Atacama occupies 105,000 square kilometres (41,000 sq mi) composed mostly of salt lakes (salares), sand, and felsic lava flows towards the Andes. The Atacama Desert is commonly known as the driest place in the world, especially the surroundings of the abandoned Yungay town (in Antofagasta Region, Chile). The average rainfall is about 15 millimetres (0.59 in) per year, although some locations, such as Arica and Iquique receive as little as 1 millimetre (0.04 in) to 3 millimetres (0.12 in) in a year. Moreover, some weather stations in the Atacama have never received rain. Periods of up to four years have been registered with no rainfall in the central sector, delimited by the cities of Antofagasta, Calama and Copiapó, in Chile. Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971. The Desert is probably also the oldest desert on earth and has experienced extreme hyperaridity for at least 3 million years, making to it the oldest continuously arid region on earth. The long history of aridity raises the possibility that supergene mineralisation, under the appropriate conditions can form in arid environments, instead of requiring humid conditions. Geological research suggests that in some sections of the Atacama Desert, such as in today's Chile, hyperaridity has persisted for the last 200 million years (since the Triassic). This desert is so arid that many mountains higher than 6,000 metres (20,000 ft) are completely free of glaciers; indeed, only the highest peaks (such as Ojos del Salado, Pissis, and Llullaillaco) have some permanent snow coverage. The southern part of the desert, between 25°S to 27°S, may have been glacier-free throughout the Quaternary (including during glaciations), though permafrost extends down to an altitude of 4,400 metres (14,400 ft) and is continuous above 5,600 metres (18,400 ft). Studies by a group of British scientists have suggested that some river beds have been dry for 120,000 years. However, some locations in the Atacama receive a marine fog known locally as the camanchaca, providing sufficient moisture for hypolithic algae, lichens and even some cacti—the genus Copiapoa is notable among these. Geographically, the aridity of the Atacama is explained by it being situated between two mountain chains (the Andes and the Chilean Coast Range) of sufficient height to prevent moisture advection from either the Pacific or the Atlantic oceans. The climate of the Atacama Desert limits the number of animals living permanently in this extreme ecosystem. Indeed some parts of the desert are so arid that no plant or animal life can survive. Outside of these extreme areas, sand-colored grasshoppers blend with pebbles on the desert floor, and beetles and their larvae provide a valuable food source in the lomas. Desert wasps and butterflies can be found during the warm and humid season, especially on the lomas. Red scorpions also live in the desert.

• published: 12 Dec 2013
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