New study shows that the crust in the Cradle of Humankind region has thinned to just 13 kilometers, offering a new explanation for the wealth of ancient human fossils in Turkana
A new study published inNature Communications. , suggests that the Turkana Rift in East Africa is in a more advanced stage of continental separation than previously thought. The region, which stretches between Kenya and Ethiopia, is recognized as one of the most important fossil sites for the study of human evolution, but it is also a tectonically and volcanically active region, where the African and Somali plates are moving apart at a rate of about 4.7 millimeters per year.
Using high-quality seismic data collected in collaboration with industry partners and the Turkana Basin Institute, researchers from Columbia University’s School of Climate Science and the Lamont-Doherty Institute mapped the structure of the sediments and the depth of the crustal head in the rift zone by analyzing acoustic wave reflections from subsurface layers.
The key finding is that along the rift axis, the crust is only about 13 kilometers thick, compared to more than 35 kilometers in areas far from the rift center. This is a clear sign of a process called “necking” – a significant thickening of the crust as tectonic plates stretch it, similar to the center of a taffy candy stretching from both ends.
On the way to becoming an ocean
According to the researchers, such thinning weakens the crust and increases the chance of further separation. However, this is a very slow process in human life terms. The rift began to stretch about 45 million years ago, and the current stage of thinning probably began after a period of extensive volcanic eruptions about four million years ago. The researchers estimate that it will take several more million years for the region to move on to the next stage – the formation of new ocean floor and the intrusion of water from the Indian Ocean.
The study is also important because the Turkana Rift is, according to the researchers, the first active continental rift where such a stage of crustal thickening has been identified, providing a “front row seat” to understanding how continents break apart and new ocean basins form.
The findings also have implications for the study of human evolution. More than 1,200 hominin fossils from the last four million years have been found in the Turkana region – about a third of all such fossils found in Africa. For years, it has been argued that the region was a particularly important center for the development of human ancestors. The new study suggests another possibility: Turkana may not necessarily have been a unique “evolutionary paradise,” but rather a place where geological conditions created a depression that preserved an especially rich fossil sequence.
It is hypothesized that after extensive volcanic activity about four million years ago, crustal thickening caused the rift zone to subside. Within the depression, fine sediments rapidly accumulated, which are particularly suitable for preserving fossils. In other words, Turkana's rich fossil assemblage may reflect not only a hotbed of evolution, but also exceptional preservation conditions.
The researchers emphasize that this is still a hypothesis, but it opens up a new way to connect tectonics, climate, environment, and human evolution. If we understand how plate movement changed the landscape, vegetation, and climate in East Africa, we can also better understand the conditions under which human ancestors evolved.
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