Sept. 18, 2007 — The geologic rise of the Ethiopian Plateau may have happened millions of years later than thought, and just in time to nudge along the evolution of modern humans, say the authors of a new study.
Using elevation data collected by the space shuttle, orbiting satellites and radioisotope dating of various rock layers found in the walls of the Nile River Gorge, the researchers believe they have narrowed down the timing of the final phase of the plateau's uplift to less than three million years ago.
That's just in time to cause the drying out of east Africa and the creation of the pedestrian-friendly savannas on which humans evolved.
"I think we've proved that [the Ethiopian Plateau] is very young," said Nahid Gani, a geologist at the University of Utah. She and her husband Royhan Gani, also a geologist, and Mohamed Abdelsalam of the University of Missouri, report their findings in the September issue of GSA Today, published by the Geological Society of America.
Some previous estimates of the plateau's age put its rise at around 30 million years ago — far too early for it to have directly affected the immediate ancestors of Homo sapiens, who arose in the valley just a few million years ago.
Africa is splitting apart and forming a new sea. James Williams explains.
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To arrive at the more recent date, the researchers turned the question upside down. Rather than dating the plateau's uplift directly, they studied the effects of the one thing in the region that responds instantly to any change in elevation — the Blue Nile River. Like all rivers, it naturally shifts its course as the land around it changes, to form the most natural slope from its source to the sea.
As the plateau rose, it raised the river's source and steepened the river's overall slope. That steepening made the river flow faster and with more erosive power. The result is the mile-deep Nile Gorge — what Nahid Gani refers to as the Grand Canyon of Africa.
