Southwest Arabia and the Horn of Africa represent one geomorphological, biotic and cultural sphere since at least the beginning of the last Ice Age. In this space image taken by Apollo astronauts, note the basic geomorphological units of Southwest Arabia including the coastal Tihamah, mountainous Asir, and Rub al Khali. The Jowf highlands, Ramlat Sabatayn, Hadramaut and Wadi Masilah in Yemen have been reconstituted as one major Late Pleistocene and Early Holocene river system.