Migration

Reconstructing climatic conditions during the migration of Homo sapiens out of Africa


a map of Greenland and the location of the NGRIP ice core; b Map of northeastern Africa, the Near East and southeastern Europe showing important fossil and archaeological sites; c Map of northeastern Africa showing the location of the Chew Bahir drilling site as well as important fossil and archaeological sites. Credit: Credit: F. v. Reumont / Earth & Environment Communications

The climatic reconstruction of the last 200,000 years from East Africa illustrates the living conditions of Homo sapiens when it migrated out of Africa / Homo sapiens was mobile across regions during wet phases and retreated at high altitude during dry phases

An international research team led by Prof. Dr. Frank Schäbitz has published a climate reconstruction of the past 200,000 years for Ethiopia. This means that high resolution data is now available for the period when the first 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 sediment deposited in the Chew Bahir Basin in southern Ethiopia, which is near human fossil sites. The temporal resolution of the samples, reaching nearly 10 years, revealed that from 200,000 to 125,000 years BC, the climate there was relatively humid, providing sufficient water and therefore abundant plant and animal food resources in the lowlands. lands of East Africa. From 125,000 to 60,000 years ago, it became progressively drier, and particularly dry between 60,000 and 14,000 years. The data now obtained correspond well to the 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 “Hydroclimatic changes in East Africa over the past 200,000 years may have influenced early human dispersal” appeared in Nature Earth & Environment Communications.

Scientists collect environmental information from lake sediments because, at best, sediment is released into lakes relatively continuously from the watershed through erosion. In addition to the mineral components, the sediments include organic matter and the remains of organisms living in the lake. If lake sediments from suitable lakes can be drilled, this “proxy data” can be used to draw conclusions about the environmental conditions at the time, and thus help reconstruct the climate.

From November to December 2014, researchers recovered an approximately 300-meter-long drill core from the Chew Bahir Basin in southern Ethiopia, which dries up during the dry season. The entire drill core dates back approximately 620,000 years. “This allows us to chronologically cover the entire evolutionary history of Homo sapiens in Africa. The work now published on the last 200,000 years of this drill core thus provides very good evidence of the environmental and climatic history during the migration of our ancestors, ”explained Schäbitz.

“Some of our proxies allow temporal resolution for specific decades in large sections of the core, which has not been done before for this part of Africa. This way we can capture very short term climate changes representing less than a human life, ”he said. The drill core reveals that the climate of East Africa was largely influenced by changes in solar insolation, which led to wet or dry climatic conditions. From 200,000 to 125,000 years ago, the climate was generally relatively favorable, that is to say that the lowlands provided sufficient water and therefore abundant plant and animal food resources for our ancestors.

Under such conditions, people could move relatively easily over long distances and even reach the Arabian Peninsula, as evidenced by the oldest fossil finds (around 175,000 years ago). From 125,000 to 60,000 years ago, however, it gradually dried up, then particularly dry between 60,000 and 14,000 years ago, with the lake completely drying up on several occasions.

“However, during this period in particular, quite striking short-term humidity fluctuations can also be observed, whose temporal models are reminiscent of the cold-warm climatic fluctuations known from Greenland ice cores. Thus, people who living in East Africa at that time were exposed to extreme changes in their environment, “said Schäbitz.” It is interesting to note that just over the period of 60,000 to 14,000 years, when the low East African lands were on several occasions particularly dry, numerous archaeological finds in the high altitudes of the Ethiopian mountains testify to the presence of our ancestors there.

In addition, the weapons and tools of these peoples also evolved during this period (passage from the Middle Paleolithic to the Upper Paleolithic in Africa). “We suspect that the greater ‘environmental stress’ at low altitudes has forced this development,” the scientist noted.

In addition, scientists have noted that the last major wet phase that we can see in the nucleus matches genetic findings well: it shows that our direct genetic ancestors “successfully” left Africa around 70,000 to 50 years ago. 000 years old. Their descendants probably reached southeastern Europe 50,000 to 40,000 years ago, where they encountered Neanderthals.

“We hypothesize that the evidence of dry-wet climatic fluctuations in East Africa found in our drill core had a significant impact on the evolution and mobility of our ancestors,” said Schäbitz. “Migration out of Africa has been possible on several occasions over the past 200,000 years, during times of wetter climates, and has led to the spread of our ancestors to Europe. During the particularly dry phases of the recent past, starting around 60,000 years ago, Homo sapiens groups have repeatedly managed to survive in the high altitudes of mountainous Ethiopia.

Reference: “Hydroclimatic changes in East Africa over the past 200,000 years may have influenced early human dispersal” by 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 and Martin H Trauth, June 14, 2021, Earth & Environment Communications.
DOI: 10.1038 / s43247-021-00195-7

The publication with 20 international co-authors is the result of subproject A3 of the Collaborative Research Center (CRC) 806 “Our Way to Europe” at the University of Cologne, which was granted in 2009 and cooperates closely with the Institute of prehistory and prehistory of the UoC. Ancient history as well as the universities of Bonn and Aachen. The CRC aims to understand the reasons for the migratory history of our ancestors (Homo sapiens) from Africa to Europe. The Chew Bahir Deep Drilling Project is associated with the Hominin and Paleolakes International Drilling Project (HSPDP).



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