More than one third of Asia is dry. From the Red Sea almost to the Pacific are a series of deserts and semideserts, the product of continentality, mountain patterns, and atmospheric circulation. Two areas of extreme aridity are present in die Rub al Khali of southern Arabia and the Takla Makan of western China, both essentially rainless and lifeless. Elsewhere, aridity fades off into subhumid lands with marginal potentials for settlement.