Deserts evoke images of uninhabited arid lands in which the phenomenon of life seems to be a complicated undertaking. But the truth is that they are ecosystems with their own flora and fauna and cover more than a fifth of the Earth's land surface.

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Dryness is the main characteristic of a desert. They are arid places, regardless of whether they are cold or hot, or if they are dominated by mountains or plains, rocks or sand. Of course sand is the image we most closely associate with deserts, but it covers just 20 percent of the territory worldwide that is classified as such.

The plant and animal species that live in deserts are numerous. However, they all share one trait: the ability to survive with little water. This means they have a special capacity to find and store liquid, and possess biological mechanisms that prevent water loss or evaporation.

On the Internet, deserts are present throughout the many web sites that attempt to explain the unique nature of these ecosystems, or that reflect the influence of these mysterious lands on human activity, for example, in literature.

Scientific evidence shows that deserts date back more than 100 million years. The arid conditions that caused them to appear are closely linked to climate. Today, the expansion or growth of deserts is a serious environmental problem, known as desertification.

Deserts can be found in diverse places around the world, though their sizes can vary greatly. The most extensive are the Sahara, Arabian, Gobi, Kalahari and Australian deserts.