Most researchers interested in human origins once dismissed Arabia, thinking that the peninsula was dry and empty until only a few thousand years ago. But new climate research shows that Arabia's fierce deserts were once well-watered. At intervals in the past few hundred thousand years, brown Arabia turned green, drawing animals—and ancient humans—to its lakes and rivers. Innumerable gray and brown triangular stone tools, expertly knapped by human hands, show that large numbers of our ancestors found this land a congenial home. And for early humans expanding out of Africa, Arabia sits in a crucial location. University of Oxford archaeologist Michael Petraglia suspects that humans left their home continent early and meandered slowly eastward through a temptingly wet and green Arabia, eventually reaching India. He and others are now fanning out across the kingdom of Saudi Arabia to uncover Arabia's role in ancient human dispersals.