June 27, 2011
Each season, the first day of work involves survey and setting up our excavations. Today was no exception. I gathered the entire crew of excavators, 27 Kenyan colleagues who are expert in the meticulous activity of digging with metal awls and brushes, flicking away tiny bits of dirt. That’s how our team carefully uncovers the buried fossils, stone tools, and other hints of the environment in which the toolmakers lived.
The entire group drove out to one of our more famous sites, called Site 15, where we first found an elephant butchery site. For any of you who have visited our new Hall of Human Origins at the Smithsonian, the elephant butchery is the topic of one of the ‘Snapshots in Time’ dioramas, which have been really popular with visitors to the exhibition. Since the elephant butchery was first excavated in the late 1980s, we’ve also found evidence of two other butcheries in the same excavation. These two parts of the dig were where some early humans came and used stone tools to cut meat from the bones of an antelope and a zebra, and smash open some of the bones for the nutritious, fatty marrow inside the bones.
As I explained to our team, six of our excavators last year dug a bit further into the layers of dirt and found zebra teeth, many stone flakes, and also boulders and hand-sized hammerstones. The top surfaces of the boulders, as we found them in the ground, had indentations or depressions that looked like the result of repeated pounding. At other sites we’ve dug in the Olorgesailie region, we’ve found similar depressions on the upper sides of flat-topped rocks. The depressions are filled in with hardened sediment, which protects the actual surface inside these dips in the rock. When we looked under a microscope, embedded in the surface were particles of plants – tiny bits known as phytoliths (‘plant stones’), which form between the cells of roots, leaves, stems, and fruits. The exciting thing, then, is that the butchery area of Site 15 may also hold clues to the plant foods that early humans ate. The tiny phytoliths observed back in the lab indicate that the early humans used the boulders as stone anvils, on which they crushed and prepared the plants, probably before eating them. I’ll have more to say about this when the Kenyan researcher doing the microscopic study joins us later in the season. Her name is Rahab Kinyanjui.
So our goal this season at Site 15 is to continue digging further where the concentration of boulders, hammerstones, and other stone tools were found last year. We’ll also see if the zebra teeth lead us to another butchery site of a different zebra from the first one we found some years ago.
Our group then drove down toward the dry river bed, where we usually walk across to get to younger layers of sediment. Well… life in the field always has its surprises. The surprise today is that the river bed wasn’t at all dry. Remember the rain that barely missed us yesterday? It didn’t miss the high edge of the Rift Valley to the east, and the runoff from the highlands filled the river bed that runs through the Olorgesailie region. Yet our team was undeterred – and very determined to get across. In the photo, you can see that the excavators found plenty of rocks on the surrounding landscape to make a narrow footpath across the flow.