Climate reconstruction of the last 200,000 years from East Africa illustrates the living conditions of Homo sapiens when he emigrated from Africa / Homo sapiens was supraregional mobile during the humid phases and withdrew to high altitudes during the dry phases
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 in which the early Homo sapiens, our ancestor, made their way from Africa to Europe and Asia. Schäbitz and his colleagues obtained the data from a drill core from lake sediments that had been deposited in the Chew Bahir Basin in southern Ethiopia, which is located near fossil sites of our species. The temporal resolution of the samples, accurate to a maximum of 10 years, showed that from 200,000 to 125,000 years before our time the climate there was relatively humid and offered enough water and thus abundant vegetable and animal food sources in the lowlands of East Africa. From 125,000 to 60. 000 years ago it gradually became drier, particularly dry between 60,000 to 14,000 years ago. The data that have now been determined fit well with the genetic findings known so far, according to which our direct genetic ancestors (“African Eve”) left Africa “successfully” – in a wet phase – around 70,000-50,000 years ago. The article “Hydroclimate changes in eastern Africa over the past 200,000 years may have influenced early human dispersal” appeared in Nature Communications.
The scientists collect information about the environment from the lake sediments, since in the best-case scenario sediments enter the lakes relatively continuously through erosion in the catchment area. In addition to the mineral components, organic material and residues of organisms living in the lake belong to the deposits. If it is possible to drill lake sediments from suitable lakes, these “proxy data” (English proxies) can be used to draw conclusions about former environmental conditions and thus reconstruct the climate of the past.
In November to December 2014, the researchers were able to recover an approx. 300 m long drill core from the Chew Bahir Basin in southern Ethiopia, which dried up during the dry season. In its entirety, the drill core goes back to around 620,000 years ago. “This enables us to cover the entire history of the development of Homo sapiens in Africa. The work that has now been published over the last 200,000 years of this drill core documents very well the environmental and climatic history during the expansion of our ancestors, ”explains Professor Schäbitz.
“Some of our proxies allow a decadal time resolution in large sections of the core, something that has not yet existed for this part of Africa. We use it to record very brief climatic changes that represent less than a human life, ”says Schäbitz. It can be seen that the climate in East Africa was essentially influenced by changes in the amount of solar radiation, which led to either humid or dry climatic conditions. From 200,000-125,000 years ago the climate was generally relatively favorable, ie the low-lying areas offered enough water and thus plenty of vegetable and animal sources of food for our ancestors. Under such conditions, people were able to move relatively easily and even reach the Arabian Peninsula, which is documented by the oldest fossil finds there (approx. 175,000 years ago). From 125,000 to 60,000 years ago, however, it gradually became drier, particularly dry then between 60,000 to 14,000 years ago, with the lake drying up completely several times.
“However, it is precisely during this period that very striking, short-term fluctuations in humidity can be observed, whose temporal patterns are reminiscent of cold-warm climatic fluctuations that are known from the Greenland ice cores. The people who lived in East Africa at the time were exposed to extreme changes in their environment, ”said Schäbitz. “It is interesting that in the period from 60,000 to 14,000 years, in which the lowlands of East Africa were repeatedly particularly dry, numerous archaeological findings in the high elevations of the Ethiopian mountains prove the presence of our ancestors at greater heights During this period the weapons and tools of these people were further developed (transition from the Middle to the Late Paleolithic in Africa). “We suppose,
It is also interesting that the last major wet phase, which can be seen in the examined core, fits well with the genetic findings: according to this, our direct genetic ancestors (“African Eve”) are said to have “successfully” left Africa about 70,000-50,000 years ago . Their descendants probably reached southeast Europe 50,000-40,000 years ago and met the Neanderthals there.
“We suspect that the evidence found in our drill core for dry-wet climatic fluctuations in East Africa had a significant influence on the development and mobility of our ancestors,” said Schäbitz. “The“ Out of Africa ”was possible several times over the last 200,000 years under humid conditions and contributed to the spread of our ancestors to Europe. During the particularly dry phases of the recent past, from around 60,000 years on, Homo sapiens groups have repeatedly managed to survive in the high altitudes of mountainous Ethiopia. “
The publication with 20 international co-authors grew out of the A3 subproject of the Collaborative Research Center (SFB) 806 “Our way to Europe”, which has been carried out successfully in Cologne since 2009 in close cooperation with the Institute for Prehistory and the Universities of Bonn and Aachen . The aim of this CRC is to understand the reasons for the history of the spread of our ancestors (Homo sapiens) from Africa to Europe. The Chew Bahir deep drilling project is also internationally involved in the “Hominin Site and Paleolakes Drilling Project” (= HSPDP) project.
Reference: Schaebitz, F., Asrat, A., Lamb, H.F. et al. Hydroclimate changes in eastern Africa over the past 200,000 years may have influenced early human dispersal. Commun Earth Environ 2, 123 (2021). https://doi.org/10.1038/s43247-021-00195-7
Provided by University of Cologne