An international research team led by Professor Dr Frank Schäbitz has published a climate reconstruction of the last 200,000 years for Ethiopia. This means that high-resolution data are now available for the period when early Homo sapiens, our ancestors, made their way from Africa to Europe and Asia. Schäbitz and his colleagues determined the dates using a drill core of lake sediments deposited in southern Ethiopia's Chew Bahir Basin, which lies near human fossil sites. Temporal resolution of the samples, reaching nearly 10 years, revealed that from 200,000 to 125,000 years before our time, the climate there was relatively wet, providing enough water and thus abundant plant and animal food resources in the lowlands of East Africa. From 125,000 to 60,000 years ago, it gradually became drier, and particularly dry between 60,000 to 14,000 years ago. The data now obtained fit well with genetic findings, according to which our direct genetic ancestors ('African Eve') left Africa 'successfully' during a wet phase about 70,000 to 50,000 years ago.
The article 'Hydroclimate changes in eastern Africa over the past 200,000 years may have influenced early human dispersal' has appeared in Nature Communications.
Scientists collect information about the environment from lake sediments because, in the best case, sediments are flushed into lakes relatively continuously from the catchment through erosion. In addition to mineral components, sediments include organic material and remains of organisms living in the lake. If lake sediments from suitable lakes can be drilled, these 'proxy data' can be used to draw conclusions about environmental conditions at the time, and thus help to reconstruct the climate.
Frank Schaebitz, Asfawossen Asrat, Henry F. Lamb, Andrew S. Cohen, Verena Foerster, Walter Duesing, Stefanie Kaboth-Bahr, Stephan Opitz, Finn A. Viehberg, Ralf Vogelsang, Jonathan Dean, Melanie J. Leng, Annett Junginger, Christopher Bronk Ramsey, Melissa S. Chapot, Alan Deino, Christine S. Lane, Helen M. Roberts, Céline Vidal, Ralph Tiedemann, Martin H. Trauth. Hydroclimate changes in eastern Africa over the past 200,000 years may have influenced early human dispersal. Communications Earth & Environment, 2021; 2 (1) DOI: 10.1038/s43247-021-00195-7
Reconstructions of climatic and environmental conditions can contribute to current debates about the factors that influenced early human dispersal within and beyond Africa. Here we analyse a 200,000-year multi-proxy paleoclimate record from Chew Bahir, a tectonic lake basin in the southern Ethiopian rift. Our record reveals two modes of climate change, both associated temporally and regionally with a specific type of human behavior. The first is a long-term trend towards greater aridity between 200,000 and 60,000 years ago, modulated by precession-driven wet-dry cycles. Here, more favorable wetter environmental conditions may have facilitated long-range human expansion into new territory, while less favorable dry periods may have led to spatial constriction and isolation of local human populations. The second mode of climate change observed since 60,000 years ago mimics millennial to centennial-scale Dansgaard-Oeschger cycles and Heinrich events. We hypothesize that human populations may have responded to these shorter climate fluctuations with local dispersal between montane and lowland habitats.
