- Lake sediments in 10 Ethiopian, Kenyan, and Tanzanian rift basins suggest that there were three humid periods at 2.7 to 2.5 million years ago (Ma), 1.9 to 1.7 Ma, and 1.1 to 0.9 Ma, superimposed on the longer-term aridification of East Africa. These humid periods correlate with increased aridity in northwest and northeast Africa and with substantial global climate transitions. These episodes could have had important impacts on the speciation and dispersal of mammals and hominins, because a number of key events, such as the origin of the genus Homo and the evolution of the species Homo erectus, took place in this region during that time.
