While planning a visit to the East African savanna, I thought I would read up on how old this landscape was. This led me down an exciting path of discovery through articles which connected geology, weather, and human evolution, and told me about how much more there is to see than just the Big Five. In the featured map you can see a long valley down the center of Ethiopia, ending somewhere a little south of Nairobi. Equally visible is a line of lakes along the border of Uganda and Tanzania. These are the eastern and western East African Rift Valleys.
45 million years ago, soon after India crashed into the still forming Eurasian continent, a massive plume of magma welled up from deep inside the earth near where Djibouti is today. This cracked the continential plate of Africa into three: the present day Arabian plate, and the still separating Somalian and Nubian plates. Signs of this immense geological change are visible in the creation of the Gulf of Aden, and the 30 million years old lava fields and highlands of Eritrea and Ethiopia. In geological time, this is not long before the split between monkeys and apes (hominoids). It is now believed that the geographical changes due to this initial rifting may have cause climate changes that favoured the rise of the hominoids.
The magma plume later created two bubbles below the African plate and pushed up the highlands of Kenya and Ethiopia (clearly visible in the map). About 7-10 million years ago, the heated rocks of the African continental plate began separating out, with the Nubian plate pulling west and the Somalian plate moving eastward. The land between them subsided, and the Walls of Africa rose up 3 to 4 kilometers high. The high walls blocked off wet air from the oceans, changing the climate locally, and converting forests to grasslands. This is also the time at which the split between apes and humans (hominin) took place.
Darwin thought that modern humans had arisen in the grasslands of Africa. The discovery of hominin fossils along the rift valley seemed to agree with this theory. But modern thinking is that the savanna of the rift valley and hominins evolved together as a response to geology and weather. Humans evolved in this land, and then left to settle in far corners of the world. When I go to see the annual migration in the Serengeti, or to look at the dormant volcano called Mount Kilimanjaro, or even to taste the wine grown high in Kenya’s rift valley, I will be a migrant’s child come back to marvel at the homeland that his ancestors left.