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Our transcription: While human activity can influence the expansion of arid lands on a short-term basis, more powerful geological forces are at work to change the shapes of deserts over long periods of time. Global climate changes, still poorly understood, have caused the edges of the Earth's deserts to shift by hundreds of kilometers over the past few million years. Eighteen thousand years ago, for example, the deserts of Africa were much smaller than they are today. But while the size of the world's deserts has fluctuated throughout history, one factor has remained constant. Deserts have always been regarded as hostile, extreme environments. As a result, we have tended to overlook the great beauty, wonder, and potential value of these unique regions.
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