Cradle of Humanity Older Than Thought

Sediments from an ancient lake indicate both halves of the Rift Valley formed at about the same time, 25 million years ago.

The neighborhood you grew up in never quite looks the same when you go back. The ancestral neighborhood of all humanity in East Africa went through some changes too as plate tectonics pulled the Earth's crust apart and created the Rift Valley.

The geological shift around the old homestead may have started sooner than originally thought.

"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," said Michael Gottfried, a Michigan State University geologist, in a press release.

Gottfreid participated in a study that suggested the Rift Valley's two edges formed at around the same time, whereas earlier the eastern side was thought to be 15 to 25 million years older than the western side. Sediments from an ancient lake provided evidence that both halves formed about 25 million years ago.

"A key piece of evidence in this study is the discovery of approximately 25 million-year-old lake and river deposits in the Rukwa Rift that preserve abundant volcanic ash and vertebrate fossils," said study leader Eric Roberts of Australia's James Cook University in a press release.

The change in the Earth's crust would have resulted in altitude and weather pattern changes. That changing environment may have been part of what spurred apes to evolve into humans.

"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 Gottfreid.

Some of the fossils they found in the lake sediments were from some of the oldest human relatives known from the Rift Valley.

Top image: Photo of the Rift Valley in Tanzania. Credit: Wikimedia Commons, Sachi Gahan.

Bottom image: Map showing the eastern and western sides of the Rift Valley. Credit: Wikimedia Commons, Kimdime69.