East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins

TLDR

East African early Homo sapiens evolution is mainly inferred from isolated outcrops and distant marine cores. We present the first long, continuous, high‑fidelity Lake Malawi drill core that records tropical climate change directly from the continent. The core reveals extreme aridity between 135–75 kyr, with lake volume dropping ≥95 %, more severe than the LGM, followed by a rapid shift to wetter, more stable conditions after ~70 kyr linked to orbital changes, suggesting this climate transition may have facilitated early modern human expansion.

Abstract

The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early late-Pleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after approximately 70 kyr ago. This transition to wetter, more stable conditions coincides with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but our records provide evidence for dramatically wetter conditions after 70 kyr ago. Such climate change may have stimulated the expansion and migrations of early modern human populations.