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Atacama Desert, Antofagasta Region, Chile, South America

The Atacama Desert 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 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 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. Although the almost total lack of precipitation is the most prominent characteristic of the Atacama Desert, exceptions may occur. In July 2011, an extreme Antarctic cold front broke through the rain shadow, bringing 80 centimetres (31 in) of snow to the plateau, stranding residents across the region, particularly in Bolivia, where many drivers became stuck in snow drifts and emergency crews became overtaxed with a large number of rescue calls. This phenomenon is called the altiplano winter, which can produce a little rain and abundant electrical storms, and occurs in January and February. In 2012, the altiplano winter brought floods to San Pedro de Atacama. In a region about 100 kilometres (60 mi) south of Antofagasta, which averages 3,000 metres (10,000 ft) height, the soil has been compared to that of Mars. Owing to its otherworldly appearance, the Atacama has been used as a location for filming Mars scenes, most notably in the television series Space Odyssey: Voyage To The Planets. In 2003, a team of researchers published a report in the journal Science in which they duplicated the tests used by the Viking 1 and Viking 2 Mars landers to detect life, and were unable to detect any signs in Atacama Desert soil. The region may be unique on Earth in this regard and is being used by NASA to test instruments for future Mars missions. The team duplicated the Viking tests in Mars-like Earth environments and found that they missed present signs of life in soil samples from Antarctic dry valleys, the Atacama Desert of Chile and Peru, and other locales. In 2008, the Phoenix Mars Lander detected perchlorates on the surface of Mars at the same site where water was first discovered. Perchlorates are also found in the Atacama and associated nitrate deposits have contained organics, leading to speculation that signs of life on Mars are not incompatible with perchlorates. The Atacama is also a testing site for the NASA-funded Earth-Mars Cave Detection Program. The Valle de la Luna in English, the Valley of the Moon, is another area of the Atacama Desert which is said to look like the surface of the moon. It lies 13 kilometres (8 mi) to the west of the town, San Pedro de Atacama.