The Sahara pump theory is a hypothesis that explains how flora and fauna migrated between Eurasia and Africa via a land bridge in the Levant region. It posits that extended periods of abundant rainfall lasting many thousands of years (pluvial periods) in Africa are associated with a "wet-green Sahara" phase, during which larger lakes and more rivers existed.[1] This caused changes in the flora and fauna found in the area. Migration along the river corridor was halted when, during a desert phase 1.8–0.8 million years ago (mya), the Nile ceased to flow completely[clarification needed][2][3] and possibly flowed only temporarily in other periods[4] due to the geologic uplift (Nubian Swell) of the Nile River region.