One-fifth of the Earth's land is covered by Deserts and in every continent they are found .In this region one-sixth of the Earth's population that is about more than one billion people actually are living there .Only about 10% of the deserts have sand dunes. There are two types of deserts : 1- Hot deserts 2- Cold deserts Hot Deserts: * The largest hot desert in the world is Sahara Desert. * The temperature there rises up to 50 degrees Celsius during the day but in the night it reaches up to -18 degree Celsius . * About 250 millimeters of rainfalls per year. * Animals like Camels are adapted in such a way that they can go without food and water for many days. Many of animals are nocturnal and remain underground for most of the time.Birds are carnivorous like Eagles, Vulture etc.can be seen flying around in search of prey.