Early human occupation of the Red Sea coast of
Eritrea during the Last Interglacial

Summary of article appearing in Nature Vol. 405; 4 May 2000

Article by Robert C. Walter, et al.

The fossil record points to Africa as the origin of anatomically modern humans, approximately 130,000 years before the present. Evidence of Homo sapiens has been found throughout the continent; however, until recently there was little to no reliable evidence that humans were living along the coast at this time. The lack of evidence is in part due to the fact that the African coastline has changed dramatically since the Pleistocene.

Around the end of the Pleistocene, Earth entered into the current interglacial period. One of the implications of this is that sea level around the world has risen, submerging the Pleistocene material. Research by Walter et al off the coast of Eritrea has revealed stone tools on an emerged reef terrace that can be dated to the late Pleistocene. This article describes the tools and their possible implications regarding migrations from the African continent. The tools, which include bifacial handaxes, flakes and blades where discovered in the Abdur Reef Limestone. The tool collection draws from both old and new technologies found inland. Although other tools have been found on the Red Sea Coast of Africa, researchers working on this site were able to date the material using two different methods. The first method matched the artifact layer with other outcrops of that same layer that have been dated. The layer in which the artifacts were found is known from other sites to be approximately 125,000 years old. The second dating technique measured the uranium concentrations in the coral. The technique, called thermal ionization mass spectrometry, reads the amount of certain elements present in the material. These elements, such as uranium, break down into other elements at a known rate. By calculating the ratio of one element to another, researchers can tell how old the material is. The average of the dates gathered from the coral samples is 125,000 +/- 7,000 years before the present. It is believed that stone tools also come from older coastal deposits although these cannot presently be dated with the same accuracy. The tools at the site have retained sharp edges, which is evidence that the tools were not washed into the area, and thus are not actually older or younger than the surrounding coral. They can also be associated with marine and land fossil remains, showing that the individuals who made and used the tools relied upon both land and sea for subsistence.

Unfortunately, no human skeletal material was found with the stone artifacts. So it is unknown which species made the stone tools, although it is probable that Homo sapiens made them. Walter et al discuss the reason behind what appears to be a sudden move in Southern and Eastern Africa to coastal environments and the exploitation of these environments. Although this site is one of the few to yield reliable dates, there are several sites that seem to be from similar time periods. The article suggests that the move was due at least in part to environmental changes. Earth goes through glacial and interglacial periods during which the glaciers advance and retreat, causing drastic changes in temperature, aridity, and sea level. Environmental drying in the interior of Africa may have been enough to force populations to migrate to the coast in search of sustenance. This site is believed to predate the migration of Homo sapiens off the African continent. If this is the case, it opens up the possibility that these early populations may have taken a coastal route. The authors note that more work needs to be done along the coast to test this coastal route hypothesis and the role marine resources played in the dispersal of modern humans.

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