The Birth of an Ocean
Even today, the geology of this desert caught between Africa and Eurasia remains dynamic. For instance, the Earth's crust is splitting apart along the long, narrow gash of the Red Sea, which runs between the Arabian Desert and Northern Africa. The gaps between Africa and Eurasia began opening 35 million years ago along the 1,600-mile (2,560 km) Red Sea, splitting the Middle East from Africa. This rift has played a vital role in spawning three of the world's religions and perhaps the human species itself.
Many geophysicists maintain that the Red Sea is really a young ocean, which will one day form a new basin to rival the Atlantic Ocean. The Red Sea is merely the deepest, wettest part of a system of rifts that will eventually rip loose a huge chunk of Eastern Africa, perhaps casting it adrift as a minicontinent like Australia. Geologists think that the ridge emerging under the Red Sea will split into a system of ridges dividing at least three different crustal plates. That will eventually create an ocean ridge running down Africa's Great Rift Valley.
Such rifts on the seafloor have created the Earth's terrain and ultimately control the distribution of deserts. The movement of continents embedded in crustal plates explains why a piece of land can move from junglelike conditions near the equator to areas where dry descending air creates deserts. The rift system that promises to eventually move the Arabian Desert once again runs for nearly 4,000 miles (6,400 km) from Syria through the Sea of Galilee, into the Gulf of Aqaba and the Red Sea and then on down Africa, where it splits into two rift systems. The rifted slump in the crust is marked in Africa by a series of mountains, like Mount Kilimanjaro, and deep troughs, like the ones that hold 4,500-footdeep (1,500 m) Lake Tanganyika and Lake Victoria, the second largest freshwater lake in the world.
In the low-lying deserts of these rift valleys, archaeologists have found the bones of our earliest ancestors, including the 3-million-year-old skeleton of Lucy. Experts on human evolution now believe that several types of big-brained hominids lived in the forests and savannas of east Africa. From there, they spread outward across the other continents, probably passing along the shores of the Red Sea.