Homo Erectus Exploited a River Confluence Environment Under an Arid Climate ~1 Ma, Olduvai Gorge, Tanzania

Human settlements have long prioritized fresh water sources, particularly rivers; a behaviour that has persisted since our earliest Homo ancestors. Olduvai Gorge, Tanzania is a world-renowned archeological site where fossil fauna and stone tools have shaped our understanding of human origins. Here, we reconstruct the paleoenvironment of Bed III (~1.0 Ma) at Engaji Nanyori to demonstrate an ancient river confluence where a long-lived hominin occupation accumulated a rich archeological assemblage.

The Olduvai Basin is a rift-shoulder setting that developed on the western margin of the Gregory rift in the East African Rift System during the Pleistocene. The Ngorongoro Volcanic Highlands contributed volcaniclastic material from the southeast and the exposed basement rocks contributed sediment from the west. We combine field-based data, including measured stratigraphic sections, with petrography, electron microprobe analysis, and Ar–Ar dating of tuffs to characterize the archeological discovery temporally and spatially.

We find that deposition in 1 m deep and 20 m wide fluvial channels flowing from the west constructed a series of channel-belt complexes with a basement-derived provenance. Flowing from the southeast, channels of similar scale deposited isolated channel belts with a volcanic-derived provenance. Paleoclimate reconstructions from paleobotany and geochemical proxies indicate an arid climate where fresh surface water was scarce. Therefore, we propose that Homo erectus utilized a river confluence environment to maximize the likelihood of freshwater availability from two distinct drainage basins. Our results refine our understanding of early Homo habitat and behaviour at a crucial time in human evolution.