Now that's what I call a sandpit! Time to take a hike, hot- footing it through the world's deserts 174 msafiri COOL FOR KIDS Hot stuff… According to geographers, a desert is anywhere that receives less than 25cm of rainfall a year. That means, amazingly, that around a third of the Earth's surface is classified as desert! But deserts aren't all sand dunes and palm trees. Only about a fifth of the world's deserts are actually covered in sand – most are rock, stone and scrub. And of course we all know that deserts can get scorchingly hot during the day, but did you know that they're often freezing cold at night – even in the Sahara? There are also ' cold' deserts such as the Tibetan plateau. Deserts also have a reputation for being extremely inhospitable and supporting very little life. In fact, they often have surprisingly high levels of biodiversity, including loads of lizards, and hardy plants like prickly pears and cactuses. Desert people You've got to be tough to live in the desert. There's hardly any water, very few other people, plenty of sandstorms, and summer temperatures which can top 50° C. Some of the world's hardiest nomads can be found in the African deserts, such as the San (' Bushmen') of the Kalahari, the Berbers and Tuareg of the Sahara and the Kanembu of Chad. PRICKLY CUSTOMER Dune and dusted: amazing desert facts Q Strictly speaking, the world's largest desert isn't actually the Sahara, but Antarctica. Q The Hottest Place on Earth ever recorded was El Azizia in Libya, where the temperature reached a sizzling 57.8C on 13 September 1922. Q Whereas many of the planet's natural habitats, like reefs and rainforests, are disappearing, the world's deserts are actually growing – a process known as desertification. Q The largest sand dunes can reach heights of up to 500m – that's around one- and- a-half times the height of the Eiffel Tower. Q Desert sandstorms can last for days and move whole sand dunes, whilst duststorms can appear as a solid- looking wall of dust reaching as much as a mile high! The giant saguaro cactus of the Sonoran Desert can live up to 200 years, grow up to 15m tall and weigh 10 tons! What do you call a camel with three humps? Humphrey What do people eat in the desert? Sandwiches What's the most popular rock band in the desert? Oasis