1999 Field Season: Day 23

July 17, 1999

We have temporarily closed down site B7/8-1, pending investigation by our stratigraphy team.

Continued excavation at Site A11-10 is showing that the site is as productive as we had hoped. The crew is digging through the "C" sand layer, carefully removing this layer to the surface of the layer underneath. As each layer was formed by an event in the past, it is important at this site to excavate stratigraphically, that is, following the sediments. This way, we can associate each artifact and fossil with a particular fine layer within our target sand layer. After we are through excavating layer C, we will continue with layer B underneath.

Vincent Kimeu excavates at site A11-10.

The artifacts recovered so far are occurring in clustered areas of high density, separated by a less dense scatter of stone flakes. There is a large concentration of artifacts in the northeast corner of the site, and more pieces of fossil bone have been uncovered. The fact that the artifacts are clustered like this may be indicative of multiple visits to the site through time, where each clustering of tools and bone would correspond to a visit by the early humans.

A stone tool cluster at Site A11-10.

We also lifted bones and tools again at Site 15 this afternoon. We are excavating a paleosol layer that contains a scatter of equid (horse) and bovid (antelope) skeletons, and stone tools as well. At one point during the lift, the lighting was just right to see cut marks visible in the field. The fact that we could see them in the field is amazing. It usually requires a cleaned, prepared fossil in a lab setting with the correct lighting to see these marks. But every once in a while, conditions allow you to see them in the trenches, like today, where the sun was low in the sky, and went behind a cloud at just the right time. We are sure that these marks are not excavation marks (accidentally etched into the bones by one of our team members while digging the bone out of the sediment) because the scratches were filled in with sediments. If they had been caused in excavation, they would have been empty. Of course, we need to confirm that they were indeed caused by stone tools, and not some other factor (for example, the sharp teeth of a young hyena) by studying the marks with a scanning electron microscope (SEM).

Cut marks on specimen 18 from Site 15.