Thursday, August 25, 2011


A team of scientists at the site of Olorgesailie in the East African Rift Valley of south central Kenya, Africa, are uncovering stone tools and geological clues that may hold some answers as well as raise new questions about the evolution of early human stone toolmaking and use and the environment in which the early humans lived up to 1.2 million years ago.

Led by Dr. Rick Potts of the Smithsonian Institution's Human Origins Program and in conjunction with the National Museums of Kenya, the current efforts involve a multidisciplinary team of scientists focusing on two separate but related sites in the Olorgesailie region that have recently produced abundant evidence of early human activity likely associated with Homo erectus, an extinct ancestral human that lived in the area between 1.2 and 490,000 years ago, and later early human activity that produced a more sophisticated industry of stone tools.

Like Olduvai Gorge, Koobi Fora, and Hadar, the Olorgesailie region has long been a focus of research related to human origins. Featuring ancient sediments laid down and altered or formed over millions of years as a result of geologic activity associated with the surrounding Rift Valley as well as shifting climates, its exposed sediment beds have yielded an abundance of fossils and stone tools.
that have afforded scientists a rich array of data for studying the
emergence and habitat of these early humans.

Olorgesailie is most noted for the numerous Acheulean stone handaxes, defining one of the largest single assemblages of handaxes in the world. In addition, in June of 2003, a team led by Potts discovered a human frontal skull bone dated to between 900,000 and 970,000 years old, identified as classifiable to Homo erectus. It was
found about 1.5 km from deposits of stone handaxes found in the same layer as the fossil discovery.

Working in the shadow of an ancient volcano a short distance from their field camp, the research team has been uncovering a wealth of stone artifacts and fossil remains of animals that they hope will give them a clearer picture of life for the early humans that walked this terrain and managed to survive or adapt to a fluctuating climate and geological landscape.

One site, an elephant butchery site where 990,000-year-old fossilized elephant bones have been excavated (referred to as Site 15), yielded not only fossilized bones with cut marks, but also more than 2300 stone tools surrounding the bones. More recently, the fossil bones of zebra and antelope, as well as stone flakes, boulders and hand-sized hammerstones (stones with depressions) were found at the site. Study of phytoliths (microscopic fossilized plant remains) found embedded on the hammerstones
revealed that they were used as anvils for crushing plants, possibly for eating. Overall analysis of the finds at this site has revealed that it may have been a drying wetland environment of reeds and other marsh plants where early humans found animals to butcher for their meat and bone marrow.

The second site, called "BOK-2" has yielded Middle Stone Age (MSA) stone points found within younger layers dating from 493,000 to 220,000 years ago. The most
recent excavation there in July, 2011 uncovered more than 150 stone artifacts concentrated in a one meter square -- the densest assemblage ever found at this site. MSA stone tools are considered to be representative of a more sophisticated and diverse stone tool technology characterized by small obsidian points and retouched flakes, a package of implements that enabled greater effectiveness and efficiency in the early human hunt for and preparation of food.

These discoveries are considered significant for a number of reasons, not the least of which is that they seem to predate similar MSA stone tool assemblages found in other parts of Africa and the world that are dated to around 285,000 to 125,000 years ago. More surprising still were excavations at Olorgesailie in 2010 at a 625,000-year-old site, producing nearly one thousand stone tools, some of which showed evidence that early humans were striking small blades from carefully prepared stone cores, a technique not known to be generally used until the later, MSA period.

Says Potts of these finds, "they indicate that even during the handaxe period, early humans were beginning to hit upon a new way of knapping stone. This new approach to toolmaking involved making smaller flakes by carefully planning how you strike one stone against another.........So here's the question we are testing in our excavations: Could it be that stone tools in the layers at Olorgesailie tell us about the oldest known transition from handaxes to the Middle Stone Age? We'll need a lot of digging and evidence to know this for sure".[1]

Farther west of Olorgesailie, another related story has been unfolding. For the past decade, Potts has also been co-directing work at a site called Kanjera South on the Homa Peninsula, a land mass that extends off the southern shore of the Winam Gulf, part of Lake Victoria. Here, he and project leader Dr. Thomas Plummer of Queens College in New York have excavated stone tools and butchered animal bones associated with some of the oldest humans to have lived in a grassland environment, dating from 1.9 to 2.0 million years ago.

The tools belonged to the Oldowan industry, a comparatively simple stone tool technology and the earliest known stone tool system attributed to hominins. The Oldowan was first discovered during the 1930's by Louis S.B. Leakey at Olduvai Gorge. Analysis of the variety of materials from which the stone tools were created provided evidence that suggested that the raw materials were obtained at distances of up to 13 kilometers from the point at which they were last deposited in the form of tools. This established the longest distance at which hominins, or early humans, have transported materials for toolmaking from one point to another.

What has distinguished these excavations perhaps more than any other in the past is this research team's "paleolandscape approach" to investigation and excavation, providing a means to place their site finds within a much broader context so that they can be understood and interpreted more meaningfully within the geologic and climatological environment within which they existed. Because of this, the stone tool artifacts and fossils become stars on a bigger stage.

The excavations and research at Olorgesailie and Kanjera South are expected to continue for years into the future, with plans to share the experience with the public through ongoing updates to the Smithsonian Human Origins Program website. Interested readers and the public are invited to read more about these specific discoveries and much more at the Smithsonian Human Origins Program's Olorgesailie Field Blog.



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