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. , Profile of Na/Ca ratios. Major authigenic minerals (excluding clays, quartz, feldspar) determined by X-ray diffraction. Minerals ordered to reflect generally higher salinities to the right. b, Bayesian chronological model. 1 = Excluded 14 C date that fails to follow a monotonic ordering. 2 = Excluded 40 Ar/ 39 Ar date from a single crystal. Two chert dates from samples later found to contain secondary chalcedony were also excluded from the model. See SI for details. Fig. 3. Diatom-based environmental data. Diatoms accumulated in a meromictic lake so separate conductivity and pH transfer functions are shown for mixed, /1000) = Loss on Ignition and ignition temperatures (centigrade)

, First appearance of H. sapiens in Africa from Morocco data (16). H. sapiens dispersal: 1 = genetic data (41), 2 = fossil data (39, 40). FAD = First Appearance Datum; LAD = Last Appearance Datum. Thick dashed line shows the Mid-Brunhes Event (MBE). a, Na/Ca ratios. Decline reflects change from fresh to saline alkaline lake. b, Pollen PCA 1. Low values reflect increased aridity. c, Poaceae to aquatic pollen ratios (P-A/P+A). High values indicate wetter episodes. d, Diatom Principal Component Analysis. High values reflect benthic taxa introduced to a meromictic lake by flooding. Note that many of these flood events broadly correlate (diagonal shading) with interglacial episodes in "g". e, Insolation (1°S) from AnalySeries 2.0. High variability periods shaded. f, Northwest Indian Ocean dust record (26), Pollen stratigraphy. Selected taxa shown. Pollen PCA 1 summarizes all pollen data and shows a long-term reduction in PCA values from ?575 ka that reflects increased aridity. Poaceae increase upwards with Cyperaceae and Podocarpus declining