June 2011, Daily News

Excavations in Kenya Shedding Light on Early Human Toolmaking and Habitat

By Dan McLerran   Fri, Aug 19, 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 (pictured right) 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. 

The second site, called "BOK-2" (site 2 in location B within the OK Member, a geologic layer), 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]

Kanjera South

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. Analyses 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.

This year, Potts and his colleagues visited two other Oldowan sites in the Kanjera area that Plummer had recently discovered.  "I was really impressed at the number of fossil and stone tools finds at these sites," says Potts, "and we hope to dig at both in the coming years."[2]

Mount Homa is a mountain located in western Kenya. It forms the Homa peninsula on the southern shore of Winam Gulf , an extension of Lake Victoria. It is here that evidence of some of the earliest humans living in a grassland environment was found.  

The Big Picture

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:  

"Rather than excavating patches of sediments here and there and creating a spotty prehistoric record of random time periods," says Potts, "we decided to pinpoint specific layers of sediment and follow those layers across long distances to target where we excavate for fossils and artifacts. So far, we’ve conducted hundreds of excavations throughout various time periods and geographic locations to create a continuous and gradual reconstruction of the past. The layer we are targeting now, at Site 15 [990,000-900,000 B.P.] for example, has over 130 excavations across 5 kilometers! At this point, we’ve targeted seven different time periods covering large areas of the Olorgesailie region – and about 500,000 years of time. This work allows us to create a very detailed, but also holistic, picture of prehistoric Olorgesailie."[3]

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.

Lake Manyara, a shallow lake in the Natron-Manyara-Balangida branch of the Great Rift Valley in Tanzania, is a modern-day example of the way the ancient lake environment in the Olorgesailie region may possibly have appeared when early humans traversed the area. Scientists theorize that early humans may have inhabited the higher ground away from the lake edge for protection and strategic view of the game below. 

Information for this article was obtained from the rich narrative provided through daily dispatches published for public view in the Olorgesailie Field Blog.

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Notes:

[1] Day 6 (July 1, 2011): Day at the Museum, Olorgesailie Field Blog, Olorgesailie Field Season, The Human Origins Program, Smithsonian National Museum of Natural History.

[2] Day 21 (July 16, 2011): Near the Dawn of Technology on the Homa Peninsula, Olorgesailie Field Blog, Olorgesailie Field Season, The Human Origins Program, Smithsonian National Museum of Natural History. 

[3] Day 10 (July 5, 2011): Olorgesailie -- The Big Picture, Olorgesailie Field Blog, Olorgesailie Field Season, The Human Origins Program, Smithsonian National Museum of Natural History.

Cover Photo, Top Left: Homo erectus fossil skull, courtesy Urville Djasim, Wikimedia Commons.

Photo, second from top, right: View of the Great Rift Valley in Africa. Courtesy Sachi Gahan, Wikimedia Commons.

By Dan McLerran

As Founder and Editor of Popular Archaeology Magazine, Dan is a freelance writer and journalist specializing in archaeology.  He studied anthropology and archaeology in undergraduate and graduate school and has been an active participant on archaeological excavations in the U.S. and abroad.  He is the creator and administrator of Archaeological Digs, a popular weblog about archaeological excavation and field school opportunities.