The crust beneath the Turkana Rift has thinned to about 13 kilometers, placing the region in an advanced stage of continental rifting called necking. The transition appears to have accelerated around 4 million years ago, when deformation became concentrated and sediment began accumulating more rapidly. Those tectonic changes may help explain why Turkana preserves one of the world’s richest and most continuous records of early human evolution. A 13-kilometer-thick strip of crust beneath northern Kenya may mark one of the clearest places on Earth where a continent is progressing toward breakup. The crust beneath the Turkana Rift is thinner than scientists had recognized, according to research published in Nature Communications. The work identifies Turkana as the first active continental rift known to be undergoing necking, when stretching becomes concentrated before separation. The finding also offers a new way to view Turkana’s record of human evolution. The same tectonic process that weakened the continent appears to have created sediment-filled basins capable of preserving fossils over millions of years. Late Miocene fossil-bearing strata of Lothagam in West …