Including semi-desert regions, with their sparse plant life, around one third of the earth’s landmass consists of these hot, arid wildernesses. They are usually extensive plains of rock or debris and vegetation-free mountain ranges; sand dunes cover only around 12 per cent of all deserts.
Deserts are created by cold as well as by heat. Covering around 14 million square kilometres, Antarctica, for example, is the largest desert in the world. Precipitation there is as rare as in the Sahara. Only 20 to 30 millimetres of rain falls, in the form of snow, in the centre of the continent each year, compared to an average precipitation in central Europe of up to 1,600 millimetres.
