March 28, 2012
New Age Suggested For East African Rift
A new study published in the journal Nature Geoscience is suggesting that the human species may have taken much longer to evolve thanks to plate tectonics that changed Africa´s landscape millions of years before experts previously believed.
Scientists from James Cook University, Ohio University, and Michigan State University said their findings show evidence that a major tectonic event occurred in East Africa as far back as 25 - 30 million years ago, reshaping large rivers such as the Congo and the Nile and creating the Great Rift Valley.
This geological time shift may have happened sooner than we previously thought, said Michael Gottfried, a geologist with Michigan State University.
“We now believe that the western portion of the rift formed about 25 million years ago, and is approximately as old as the eastern part, instead of much younger as other studies have maintained,” Gottfried said. “The significance is that the Rift Valley is the setting for the most crucial steps in primate and ultimately human evolution, and our study has major implications for the environmental and landscape changes that form the backdrop for that evolutionary story.”
Gottfried was part of an international team of scientists led by Eric Roberts of James Cook University who also added that the findings have “important implications for understanding climate change models, faunal evolution and the development of Africa's unique landscape.”
Scientists originally believed that the East African Rift´s eastern branch, which passes through Ethiopia and Kenya, was much older than the western branch, which forms a giant arc from Uganda to Malawi. The eastern branch was believed to have formed 15 to 25 million years before the western branch. But the team´s findings do not concur with this theory.
The study provides key evidence that the two rift segments actually developed much closer together time wise, nearly doubling the initiation age of the western segment and the timing of uplift in this area of East Africa.
A major finding in the study was the “discovery of approximately 25 million-year-old lake and river deposits in the Rukwa Rift that preserve abundant volcanic ash and vertebrate fossils,” Roberts noted. “℠Fingerprinting´ of these sediments reveals important information about when rifting and volcanism began in the western rift and how the landscape developed.”
Nancy Stevens of Ohio University added that the river deposits contained some of the earliest anthropoid primates yet found in the rift.
“This formation is the only late Oligocene terrestrial fossil-bearing deposit known from continental Africa below the equator,” said Stevens, who leads the paleontological team focused on the Oligocene, a geological period 23 to 34 million years ago.
“It has already produced several species new to science, and is particularly significant because it provides a last snapshot of the endemic African forms prior to large-scale faunal exchange with Eurasia later in the Cenozoic,” she said.
The change in Earth´s crust would have resulted in altitude and weather pattern changes. The changing environment may have been a piece of the puzzle needed to spur apes to evolve into humans, the researchers noted.
“The significance is that the Rift Valley is the setting for the most crucial steps in primate and ultimately human evolution, and our study has major implications for the environmental and landscape changes that form the backdrop for that evolutionary story,” said Gottfried.
“Although this work was initiated to help constrain the age of rocks in the Rukwa Rift Basin of southwestern Tanzania, it has provided novel data that address a number of other, large-scale phenomena that have shaped the surface of the region and the continent,” said Patrick O'Connor, associate professor of anatomy in Ohio University´s Heritage College of Osteopathic Medicine.
The research was funded by the US National Science Foundation, the Louis B. Leakey Foundation and the National Geographic Society.