The Atacama Desert is a virtually rainless plateau in South America, covering a 600-mile (1,000 km) strip of land on the Pacific coast of South America, west of the Andes mountains. The Atacama desert is, according to NASA, National Geographic and many other publications, the driest desert in the world, due to the rain shadow on the leeward side of the Chilean Coast Range, as well as a coastal inversion layer created by the cold offshore Humboldt Current. The Atacama occupies 40,600 square miles (105,000 km2) in northern Chile, composed mostly of salt basins (salares), sand, and lava flows.

Setting

The Atacama Desert ecoregion, as defined by the Worldwide Fund for Nature (WWF), extends from a few kilometers south of the Chile-Peru border to about 30° south latitude. To the north lies the Sechura Desert ecoregion, in Peru, whilst to the south is the Chilean Matorral ecoregion. The National Geographic Society considers the coastal area of southern Peru to be part of the Atacama desert, including the deserts south of the Ica Region.

To the east lies the less arid Central Andean dry puna ecoregion. The drier portion of this ecoregion is located south of the Loa River between the parallel Sierra Vicuña Mackenna and Cordillera Domeyko. To the north of the mentioned river lies the Pampa del Tamarugal.

The driest desert

The Atacama is one of the driest places on Earth, and is virtually sterile because it is blocked from moisture on both sides by the Andes mountains and by the Chilean Coast Range. A coastal inversion layer created by the cold Humboldt Current and the anticyclone of the Pacific is essential to keep the climate of the Atacama dry. The average rainfall in the Chilean region of Antofagasta is just 1 millimetre (0.04 in) per year. Some weather stations in the Atacama have never received rain. Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971. It is so arid that mountains that reach as high as 6,885 metres (22,589 ft) are completely free of glaciers and, in the southern part from 25°S to 27°S, may have been glacier-free throughout the Quaternary, 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.

Some locations in the Atacama do receive a marine fog known locally as the Camanchaca, providing sufficient moisture for hypolithic algae, lichens and even some cacti. But in the region that is in the "fog shadow" of the high coastal crest-line, which averages 3,000 metres (10,000 ft) m height for about 100 kilometres (60 mi) south of Antofagasta, the soil has been compared to that of Mars. Due 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. The desert was also prominently featured in the 2008 James Bond film Quantum Of Solace.

In 2003, a team of researchers published a report in Science magazine titled "Mars-like Soils in the Atacama Desert, Chile, and the Dry Limit of Microbial Life" 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.

credited to wikipedia