July 12, 1999
Today, we closed down the A11-20 site, after finishing the last spit. In its place two new sites were opened, A11-15 and A11-30. A11-15 is a new site that is roughly halfway between the A11-20 site that we just completed and A11-10 (the site that is requiring the immense amount of digging). A11-30 is an old excavation that was covered over last season when it was not completed.
You may notice that we are excavating a lot of sites beginning with "A11" (you will recall that A11 stands for: Locality A, Member 11)This is a function of our landscape approach to the archaeology of the Olorgesailie Basin.
When Louis Leakey began excavations at Olorgesailie in 1947, the objective was to uncover dense concentrations of stone tools at whatever stratigraphic levels they occurred. At the time little was known of the stone tool technologies of early humans, and so this approach made sense. However, do pockets of tools and fossils isolated in space and time really tell us much about how early humans interacted with their environment? As the questions in archaeology change, so do the approaches to answering them.
The landscape approach involves considering an individual layer throughout the basin. Crucial to understanding this approach is that in the Olorgesailie Basin, the sediments that are now buried meters below the surface of the earth once made up the landscape upon which plants and animals (including early humans) lived. In the case of each of the A11 sites, we are following a specific layer (our "target interval") designated UM11'-S (or the "Upper Member 11' Sand"). At each site our goal is to excavate this layer and to document all fossil bones and stone tools in it. Each excavation is a point sample. When enough point samples have been taken across the basin, we can begin to discern what the environment was like and what early humans were doing at the time when this layer comprised the ancient landscape.
One of the things that we are beginning to understand about the early humans in the area is that they preferred the sandy areas near the lake shores to muddier areas. We see high densities of stone tools in the sandier areas, and where the sandy areas give way to the lake shore mudflats, the stone tools disappear. We are seeing this pattern repeat itself as we uncover more sites. From this pattern we are getting clues about the environments favored by our early human ancestors.
Then we try to compare different landscapes from different time periods. In this way we can see how the environment and landscape changed over time and also how the early humans responded to different environments. This is one way to study human evolution.