...The East African Rift Valley, as the region is known, formed where the Somalian and Nubian plates are pulling away from the Arabian Plate. The eastern branch of the rift passes through Ethiopia and Kenya, and the western branch forms a giant arc from Uganda to Malawi.

The eastern branch formed around 25 to 30 million years ago, whereas the western branch formed only 10 to 15 million years ago — or at least that's what scientists  thought. Now, new evidence points to an earlier birth date for the western branch, too. [Have There Always Been Continents?]...