A desert is a landscape or region of land that is very dry because of low rainfall amounts (precipitation), often has little coverage by plants, and in which streams dry up unless they are supplied by water from outside areas. Deserts can also be described as areas where more water is lost by evapotranspiration than falls as precipitation. Desert plants must have special adaptations to survive with this little water. Deserts take up about one third (33%) of the Earth's land surface. Bottomlands may be salt-covered flats. Eolian processes are major factors in shaping desert landscapes. Polar deserts (also seen as "cold deserts") have similar features, except the main form of precipitation is snow rather than rain. Antarcticais the world's largest cold desert.The driest place on Earth is the Atacama Desert. It is virtually devoid of life because it is blocked from receiving precipitation by the Andes mountains Plants face severe challenges in arid environments. Problems they need to solve include how to obtain enough water, how to avoid being eaten and how to reproduce. Many desert plants have reduced the size of their leaves or abandoned them altogether. Cacti are desert specialists, the leaves have been dispensed with and the chlorophylldisplaced into the trunks, the cellular structure of which have been modified to allow them to store water. Deserts are increasingly seen as sources for solar energy, partly due to lower cloud cover. Many successful solar power plants have been built. Mars is the only planet in the solar system on which deserts have been identified. Despite its low surface atmospheric pressure, the patterns of atmospheric circulation on Mars have formed a sea of circumpolar sand, much larger than deserts on Earth.
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