Deserts are forms of landscape that receive little rainfall. For a region to be classified as a desert, it needs to receive less than 250 mm (10 inches) of rain per year, in addition to observing the its level of evapotranspiration, that is, the combination of water loss by atmospheric evaporation of water from the ground together with the loss in the form of steam.
Due to the fact that they are quite arid, there are few species of life that manage to develop in deserts, even more so if we compare these landscapes with other wetter regions. The fauna is predominantly formed by rodents, reptiles and insects. Both animals and plants show efficient adaptations to desert conditions; some animals need minimal amounts of water.
As previously mentioned, these regions are basically classified as arid, when they present less than 250 millimeters of rain per year; and extremely arid, when they have at least 12 consecutive months without rain. There are different types of deserts, such as polar deserts, which are covered by snow and have annual precipitation of less than 250 mm.
To get an idea, technically, the biggest desert in the world is not the Sahara Desert, but Antarctica. Some deserts are very suitable for the extraction of minerals, such as copper, in the deserts of the USA, Chile, Peru and Iran; iron, lead and zinc in Australia, etc. Although there are no large deserts in Brazil, there is evidence to show that this type of landscape was found on a large scale in Bahia millions of years ago.