Horn of Africa displays the greatest diversity, a sign often viewed to represent a geographic origin. The Horn of Africa is also the place where the haplogroup E1b1b originated from, Christopher Ehret and Shomarka Keita have suggested that the geography of the E1b1b lineage coincides with the distribution of the Afroasiatic languages. Genetic analysis done on the Afroasiatic speaking population further found that a pre-agricultural back-to-Africa migration into the Horn of Africa occurred through Egypt 23,000 years ago and it brought a non-African ancestry dubbed Ethio-Somali in the region. Together with northern Somalia, Djibouti, the Red Sea coast of Sudan and Eritrea is
Horn of Africa single landmass around 18 million years ago, before the Gulf of Aden rifted and separated the Horn region from the Arabian Peninsula. The Somali Plate is bounded on the west by the East African Rift, which stretches south from the triple junction in the Afar Depression, and an undersea continuation of the rift extending southward offshore. The northern boundary is the Aden Ridge along the coast of Saudi Arabia. The eastern boundary is the Central Indian Ridge, the northern portion of which is also known as the Carlsberg Ridge. The southern boundary is the Southwest Indian Ridge. Extensive glaciers once