Organic geochemical perspectives on hydrothermalism at Olduvai gorge, 1.7 Mya

Landscape-scale geochemical reconstructions within the cradle of humanity may yield insights into the evolutionarily-relevant relationships between early hominins and their changing environments. While current geological interpretations of Olduvai Gorge 1.7 Mya suggest the presence of precession-driven wet-dry cycles atop a general aridification trend, the local environments early hominins experienced may have been varied and dynamic. Here, we analyse biomarkers to study the paleolandscape of a single deposition event, the 1.7 Myr old, Lower Augitic Sandstone (LAS) Bed II, at Olduvai Gorge. The discovery of the coexistence of two sets of stone tool technologies, Oldowan and Acheulean, during this depositional event at archaeological sites HWK and FLK-W, has revitalized the hypothesis that these hominin technologies may have been related to the exploitation of specific local resources. New geochemical evidence from LAS sediments suggests the presence of resource-rich mosaic ecosystems, with groundwater-fed rivers and aquatic plants, revealed by the structural and isotopic characteristics of lipid biomarkers from microorganisms and vegetation. In this study, we employ data from lipids to illustrate an Olduvai environment populated by C3 aquatic plants and angiosperm shrublands, as well as plants that may have been edible. We also found an unusual biomarker distribution of monoalkyl glycerol monoethers (MAGEs), isoprenoids, and fatty acids, consistent with the presence of hydrothermal features, which may have influenced early hominin behaviour. Similar distributions are reflected at active hydrothermal environments at Yellowstone National Park and New Zealand, though the study of hydrothermalism in ancient settings and its influence on hominin evolution has not yet been addressed. The hydrothermal features suggested by lipid biomarkers at Olduvai Gorge may have enabled early hominins to thermally process edible vegetation and animal matter, thus supporting the possibility of a pre-fire stage of human evolution.