Fig. 1.

Present day precipitation patterns during long rains (A; March to May) and short rains (B; October to December) (75). Bold horizontal lines mark the ITCZ. The IOC (B; dashed line) is prominent during short rains, and its eastward displacement correlates with higher seasonal precipitation (66). Targets show Olduvai Gorge’s location (●, ODP site 662; ○, ODP site 722). (C) Depositional environments at Olduvai Gorge during the early Pleistocene about 2.0–1.8 Ma. Expanded and contracted lake levels are reconstructed based on detailed stratigraphic correlations (11, 12, 43).