March 26, 2012: - The huge changes in the earth’s crust that shaped the face of the African continent are being re-defined according to research published in Nature Geoscience today.
The Great Rift Valley of East Africa – the birthplace of the human species – may have taken much longer to develop than previously believed.
Lead author Dr Eric Roberts, from James Cook University (JCU) in Australia, said that the findings have important implications for understanding climate change models, faunal evolution and the development of Africa’s unique landscape.
“Contrary to existing models that cite rapid onset of uplift in East Africa over the last few million years as the trigger for climate and environmental changes in Africa that helped drive human evolution in Africa, our findings suggest a much more prolonged history of rifting and uplift in East Africa,” Professor Paul Dirks, one of the co-authors of the paper, said.
Professor Dirks is Head of the School of Earth and Environmental Sciences at JCU.
The Rift is an example of a divergent plate boundary, where the Earth’s tectonic forces are pulling plates apart and creating new continental crust.
The East African Rift system is composed of two main segments, the Eastern branch that passes through Ethiopia and Kenya, and a Western branch that forms a giant arc from Uganda to Malawi, interconnecting the famous rift lakes of eastern Africa.
Traditionally, the Eastern Branch is considered much older, having developed 15-25 million years earlier than the Western Branch.
The international research investigation led by Dr Roberts provides new evidence that the two rift segments developed synchronously, nearly doubling the initiation age of the Western branch and the timing of uplift in this region of East Africa.
“A key piece of evidence in this study is the discovery of an approximately 25 million year old lake and river deposits in the Rukwa Rift (a segment of the Western Branch) that preserve abundant volcanic ash and vertebrate fossils,” Dr Roberts said.
These deposits include some of the earliest anthropoid primates yet found in the rift.
“‘Fingerprinting’ of these sediments reveals important information about when rifting and volcanism began in the Western rift and how the landscape developed,” Dr Roberts said.
Study co-authors Dr. Richard Armstrong from ANU and Dr. Tony Kemp from UWA applied radiometric dating techniques of ash beds in the Rukwa Rift that indicate that the Western Branch became active by at least 25 million years ago.
Palaeontologist and study co-author Dr. Nancy Stevens from Ohio University has been studying new fossil material recovered from these sediments.
“So far, work in the Oligocene portion of the Rukwa Rift had revealed a rich assemblage of novel vertebrate and invertebrate species,” she said.
“This provides a unique window into the evolution of the modern African fauna, suggesting great potential for further discoveries,” she said.
The findings imply that broad uplift of the East Africa occurred as far back as 25-30 million years ago, re-arranging the flow of large rivers like the Congo and the Nile to create the unique landscapes and climates that mark Africa today.
Issued: March 26, 2012
JCU Media Liaison, Jim O’Brien 07 4781 4822 or 0418 892449