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Savanna Landscape, Kenya (Image 1)

A savanna landscape of tree-dotted grassland in Samburu National Reserve, Kenya

A savanna landscape of tree-dotted grassland in Samburu National Reserve, Kenya. The more heavily vegetated area in the middle distance is the corridor of the Ewaso Ngiro River. A University of Utah (U)-led study concluded that savanna was the predominant ecosystem during the evolution of human ancestors and their chimp and gorilla relatives in East Africa.

Researchers working on the study developed a new method that uses fossil soils to determine the amount of tree cover that existed in prehistoric landscapes. The new method was developed by correlating carbon isotope ratios in 3,000 modern soil samples with satellite photos of tree and vegetation cover at 75 tropical sites worldwide--with half in Africa--and representing everything from closed forest to open grassland. This allowed the scientists to determine the percentage of tree and woody shrub cover millions of years ago based on carbon isotope ratios in fossil soils known as paleosols.

"We've been able to quantify how much shade was available in the geological past," says Thure Cerling, a U distinguished professor of geology and geophysics, and biology, "and it shows there have been open habitats for all of the last 6 million years in the environments in eastern Africa where some of the most significant early human fossils were found."

The research was supported by the National Science Foundation and the Leakey Foundation. To learn more, see the U news story Six million years of savanna. [Research supported by NSF grants BCS 06-21542, EAR 06-17010, EAR 09-37819 and BCS 03-21893.] (Date of Image: July 2007) [Image 1 of 2 related images. See Image 2.]

Credit: Thure Cerling, University of Utah

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