A Wall Rises and New Species Evolve
Although the Wall of Africa started to form around 30 million years ago, recent studies show most of the uplift occurred between 7 million and 2 million years ago, just about when hominins split off from African apes, developed bipedalism and evolved bigger brains, the Ganis write.
Nature built this wall, and then humans could evolve, walk tall and think big, says Royhan Gani. Is there any characteristic feature of the wall that drove human evolution?
The answer, he believes, is the variable landscape and vegetation resulting from uplift of the Wall of Africa, which created a topographic barrier to moisture, mostly from the Indian Ocean and dried the climate. He says that contrary to those who cite global climate cycles, the climate changes in East Africa were local and resulted from the uplift of different parts of the wall at different times.
Royhan Gani says the change from forests to a patchwork of woodland and open savannah did not happen everywhere in East Africa at the same time, and the changes also happened in East Africa later than elsewhere in the world.
The Ganis studied the roughly 300-mile-by-300-mile Ethiopian Plateau the most prominent part of the Wall of Africa. Previous research indicated the plateau reached its present average elevation of 8,200 feet 25 million years ago. The Ganis analyzed rates at which the Blue Nile River cut down into the Ethiopian Plateau, creating a canyon that rivals North Americas Grand Canyon. They released those findings in the September 2007 issue of GSA Today, published by the Geological Society of America.
The conclusion: There were periods of low-to-moderate incision and uplift between 29 million and 10 million years ago, and again between 10 million and 6 million years ago, but the most rapid uplift of the Ethiopian Plateau (by some 3,200 vertical feet) happened 6 milli
|Contact: M. Royhan Gani|
University of Utah