July 14, 2004
What happens to artifacts after they are exposed by excavation? I briefly described a lift last week, but I wanted to go into more detail. How we remove artifacts from their original position is a very important part of what we do here, since we're not only interested in the artifacts themselves, but also what other information about hominin behavior they can give us.
In the process of excavating things and removing them for study, we inevitably destroy the ancient organization of things. So we have to be especially careful when gathering information. If we mess up in the records we keep, it's almost impossible to return, put the artifacts back in their original positions and see how they relate to the original sediments. It's kind of like formatting a disk or a hard drive on your computer. Once you do it, all of the information on that disk is lost, so you'd better have made a good record of what you had.
The first way we take care of the objects is to dig carefully so as not to break anything. Even though the bones have been fossilized, meaning the organic material has been replaced with minerals, the fossils at Olorgesailie are quite brittle and easy to break. Whenever we find a bone during excavation, we gently coat it with a thin liquid preservative, which seeps into tiny cracks and keeps the bone all in one piece.
The second way we take care of the excavated objects is by taking photographs - lots and lots of photos that show exactly what layer we're digging in when objects are discovered. The photos give us a record of how the objects we see are related to one another and what layer they were in. Each object was originally surrounded with sediment, and we record in our excavation book the exact type of sediment (fine silt, course sand, color of the sediment) for each object. Even more important is that we measure very precisely exactly how each object is positioned in the sediment. We use some special instruments to take these measurements. So when we've dug for two or three days and there are plenty of artifacts and fossils that are exposed, I call for a lift.
During a lift, I assign each artifact and fossil a unique number so that it can be individually described and recorded as we remove it from its original place. For objects that have a long side and essentially a flat bottom, we measure the dip and orientation of each find. The dip is the angle in which the artifact sits in the ground (a dip of zero means its bottom surface is perfectly horizontal). The orientation is the direction of the dip (the direction of the lowest point). We measure the dip and the direction of dip with a special compass, as you can see in the photograph. Everyone on the excavation team gets involved, as one person gently lifts the object, another wraps it in tissue and puts it in its own plastic bag, and another person writes the basic information about the object on each bag.
The exact position of the object is measured with a surveyor's laser transit. A laser transit is a machine that shoots a beam of light to a prism. The prism is held on the surface of the sediment exactly where we have just lifted an object. The light bounces off the prism and back to the laser transit, where the computer inside the transit calculates the distance and the angle to the prism. From the distance and angle, the computer then calculates the exact North coordinates, East coordinates, and elevation. These coordinates represent the unique position of each object we remove. (See the photographs above and below for the laser transit and the prism.)
In the 1980s, we set up a single coordinate system (or grid) for the entire Olorgesailie region. This means that the objects in any one excavation can be related to objects excavated anywhere else in the region. It's very important for our work because our aim is to study the entire ancient landscape and how the hominins were active throughout the area. By seeing how sites in one place compare to ones elsewhere in the region, we can investigate the places the early humans favored, the places they avoided, and the clues of their activity over the entire landscape.