29 June 2004
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Three main excavations are under way right now. One is called AD5/7-1, and that's the hominin fossil site. Another is called CL1-1, which has unearthed a concentration of stone handaxes near the Site Museum. And the other is called Site 15, which we mentioned earlier as the place of an elephant, gazelle, and possible zebra butchery. Although Olorgesailie is famed for its great concentrations of handaxes, many of our excavations look for smaller groupings of stone tools and animal bones that give us a somewhat simpler record of early human activity and preservation of the remains. In most cases, the handaxe accumulations occur due to many complex events - matters of both hominin behavior and geological processes. We'll talk about that again another day.
To begin here, let me explain the names of the sites we're currently digging. Site 15 has an easy name - it's just a number. The reason is that it's part of a large series of excavations that we began in our very first field season, in 1986. Our original goal was to focus on one target layer, an ancient soil (or paleosol) in upper Member 1. This was the beginning of a new style of excavation. Rather than digging one site containing a large cluster of stones and bones all in one spot, we decided to dig many sites along a single, thin layer. The purpose was to discover how early humans used an entire landscape - or at least a several kilometer stretch of it that we could follow and excavate along an erosion slope. The stone tools, of course, were our guide as to where early humans were active on that landscape, over the course of maybe 500 to 1000 years when that soil was forming. Sometimes we found absolutely nothing in some of our excavations, but this told us something interesting, since these places where early humans avoided stood in contrast with the real "hot spots" of activity.
In our original survey, we marked off areas as we walked along the paleosol layer, and at number 15 the top of a fossilized elephant femur (thigh bone) had eroded out from the layer. Since it was exposed on the erosion slope, it was easy to spot, and a couple days later we began an excavation there. It became Site 15. Over several seasons of excavation, we found most of the elephant skeleton, over 2300 stone artifacts with it, and butchery cut marks on the elephant's ribs. We keep digging on digging at Site 15, and we keep finding interesting things. We'll see what happens this year.
Since those first years, we've expanded our digs to many different layers. So we needed a way to keep track of where and in what geological members the new excavations were located. We decided to use a combination of letters and numbers. These give the area, the geological member, and the excavation number of the site. For example, CL1-1 means the site is in Locality C (the region near the Site Museum); the target layer with the stone tools is in Lower Member 1; and it's the first excavation we've done there - in Locality C and Lower 1. This may sound complicated, but it works really well for any researcher who hears the site name; they know immediately the general vicinity of the site and the time frame.
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Near the end of yesterday, we visited CL1-1. It's located geologically between the earliest record of sediments at Olorgesailie, 1.2 million years ago, and an volcanic ash dated at 992,000 years old. For the past two seasons, we've collected the handaxes that have eroded out of the walls of a dry stream bed just below where we're digging. CL1-1 is a small trench for now, a little over a meter back from the top edge of the modern stream bed. We're digging to find handaxes in situ, which means in their original context. You may wonder why we're going to all that effort when we could just wait for the next rains to erode more axes on to the ground. In fact, we're interested not just in having the artifacts. They can only give us a little bit of information about the people who made them. We want to find out where exactly the handaxes were found, maybe in an older stream bed or on the ancient lakeside, and perhaps at an animal butchery site or a tool manufacturing site. We're interested in context, the evidence that occurs along with the handaxes. That way, we can get information about the environment and activities associated with the handaxes and, potentially, the lifestyles of the early humans who made the tools. In our research, context is really critical to know about.
In the afternoon, I had to leave for Nairobi to prepare for the release of the article in Science about our early human fossil discovered last year at Olorgesailie. On arriving in the city, I checked email and answered questions from reporters who already knew about the paper, which comes out this Friday. To be honest, I'd rather be with the rest of the team to carry on with the digs. But the field crew certainly knows its business, as they've all been well trained and the day-to-day operations are well organized by Muteti Nume, our experienced foreman. I look forward to seeing what's going on when I return tomorrow.