Mohammed Umer Dr. Mohammed Umer Department of Earth Sciences University of Addis Ababa Ethiopia If you would like to interview this scientist, please contact Leah Christen. > biographical information > abstract > paper

Biographical Information:

I am currently teaching and researching in the Department of Earth Sciences at the University of Addis Ababa, Faculty of Sciences, Ethiopia. My main interest is the reconstruction of the environmental and climatic history of the Horn of Africa region based on lake sediments, buried soils and speleothem records. I collaborate with researchers from France, the UK and Italy. I have a grant from the INSU/CNRS (France) to undertake research on a high altitude lake sediment core from the Bale Mountains of Ethiopia and a grant from the Museum National D'Histoire Naturelle (France) for research on material from the Fejej prehistoric site. START, through its Visiting Scientist Fellowship Program funded my stay at the University of Wales at Aberystwyth, and the Royal Society (UK) also assisted me to establish links with the University of Newcastle for Stalagmite paleoclimate research in Ethiopia.

I am a scientific steering committee member of the PAGES-PEP III transect as well as PAGES local representative for Ethiopia. I have good links to the START-PAGES regional office in Nairobi, as well as to the African Pollen Database project.

Abstract:

Climate change, human evolution and later adaptation in the Horn of Africa and surrounding regions

In the Horn of Africa, studies of environmental and climatic changes have focused on two areas: (1) understanding human origins and evolution, and (2) finding continuous evidence during the Late Quaternary. Ethiopia is one of the regions in the Horn and Eastern Africa where the oldest and most important human fossils and cultural remains have been found. However, there have been challenges to find evidence of environmental and climatic conditions during the most important stages of human evolution and later cultural developments, such as the origin of agriculture. Moreover, the influence of climate change on some of the evolutionary transitional stages, including conditions under which Homo Sapiens evolved and dispersed out of Africa, have been the subject of discussion. In addition, understanding the roles of climate change and/or human impact in modifying the environment over the last few thousand years has been important in understanding the sustainability of the present environment.

This presentation describes environmental and climatic conditions during the following stages: in relation to human origins (prior to 4M yrs), during the Pliocene Australopithecus Afaransis, during the transition from Australopithecus to Homo (at ~2.5 M yrs) and during the origin and dispersal periods of Homo Sapiens (post 200 K yrs BP). Emphasis will be placed on postglacial continuous high-resolution evidence, such as from a high altitude lake in Southern Ethiopia and from lake sediment records in the Main Ethiopian Rift Valley. They record histories of deglaciation, Early Holocene warm and moist conditions, and Early Holocene abrupt dryness. Whether the Mid to Late Holocene shift to dryness is due to a general decrease in moisture or to increased seasonality will be discussed. It is hypothesized that this condition might have influenced the late origin of agriculture on the Ethiopian highlands.

Finally, a potential site for a long coring project at Lake Tana, in the headwater of the Blue Nile in North Western Ethiopia will be highlighted. Coring and seismic evidence have indicated that the lake dried out and refilled several times during the Pleistocene.

Paper:

Climate Change, Human Evolution and Later Adaptation n the Horn of Africa and the Surrounding Regions

Did global climate change affect hominid origin, adaptation, dispersal and extinction?
Ethiopia contains one of the oldest prehistoric sites providing evidence of human origins dating back to more than 5 million years. Although global climate change can have an impact on the origin, adaptation, dispersal and extinction of hominids, clear evidence showing this relationship has so far been lacking. This is due to the presence of very limited sequences with continuous records of hominid lineages and the difficulty of obtaining precise climatic proxies, and dating problems.

Nevertheless, faunal and floral evidence is now emerging to show the environmental and climatic conditions of early hominids. One such record comes from a nearly continuous sequence of Australopithecus afarensis at Hadar, precisely dated to 3.4 to 2.9 million years. The scientists who discovered this record suggest that A. afarensis survived substantial environmental variability in generally cooler and wetter climatic conditions than today. This adaptation did not depend on high brain capacity or the ability to make stone tools.

In 1994, the Middle Awash Group described a new 4.39 Ma hominid species Ardeptitecus ramidus. Faunal and floral remains confirmed that a wooded habitat comprised the immediate environment of its early hominid occupants, probably under wetter conditions.

After about 3 to 2 Ma the evidence shows that hominid diversification was very high and the oldest stone tools were made. Floral records indicate that the climate started to become more arid than the previous time.

Lake Tana, a potential site for long climatic sequence during the emergence and dispersal of Anatomically Modern Humans (AMH)
The Earliest AMH emerged at ~200 kyr BP in Ethiopia. Faunal indicators, as well as Mediterranean sapropel data, show conditions were humid during their origin. However, the climates and environments under which AMH dispersed to other parts of the globe are still to be resolved.

Seismic survey of Lake Tana, the source of the Blue Nile, reveals the presence of >40 m of sediment with the potential to provide paleoenvironmental information for up to 200,000 years. Strong reflectors and shallow coring indicated the presence of periodic desiccation layers probably related to “Heinrich” events. The information will provide a globally significant record of climate change as well as an environmental framework for the later part of human evolution and dispersal.

Transition from hunter-gathering to early agriculture
Better records of environmental and climatic changes exist for the Late Quaternary in Ethiopia. During the Last Glacial Maximum, the Ethiopian highlands contained ice with lowering vegetation belts. Lake levels were low or even dry. Lake Tana, at the headwaters of the Blue Nile, dried at about 17 kyr BP, at the same time as Lake Victoria, indicating that the north-western Ethiopian highlands were dry. It is possible that the most humid south-western Ethiopian highlands could have accommodated the then hunter-gatherer societies. This region today holds one of the most diverse ethnic and linguistic groups in the country.

The Mesolithic to Neolithic cultural transition in low-lying areas of the region took place during the Early Holocene humid phase. Existing data from the Ethiopian highlands shows that agriculture emerged over the last 3 to 4 kyr under more seasonal rainfall conditions. It seems that when several civilizations collapsed at around 4.2 kyr BP (Egypt, Mesopotamia, Syria and Turkey), the Ethiopian highlands, with their moderate temperature, seasonal rainfall conditions and fertile volcanic soils must have provided favorable conditions for settled agriculture and animal domestication.

These highland regions, considered to be the water towers of the Horn of Africa, today hold 88% of the total population of Ethiopia. Intensive land use under highly variable climatic conditions is leading to land degradation and the consequent intermittent food shortages. New stalagmite paleoclimate research is being conducted with Dr. Andy Baker (UK), to find decadal to annual scale climate variability and cycles.

Figure 1.
Seismic evidence showing desiccation layers in Lake Tana sediments.

Figure 2.
Coring on Lake Tana.

(Figures courtesy of Lake Tana Project members: Henry F. Lamb, Paul V. Coombes, Michael H. Marshal, Mohammed Umer, C. Richard, Bates, Sarah J. Davies and Eshete Dejen)