June 27, 2004
It's Sunday, a well-deserved day of relaxation for the crew. They've all gone for lunch to Magadi, a small factory town about a 45-minute drive to the south. It's something a little different from camp life. I usually prefer to stay put to enjoy some rest, reading, and the view from camp. Jennifer and Jessica have returned, bringing Amanda Henry, who's a Ph.D. student in paleoanthropology from George Washington University, and Lynn Copes, who's going into her senior year in anthropology at Columbia University. Lynn's also a Smithsonian summer intern working with the Human Origins Program. They're excited to be here, not only to visit Kenya for the first time, but also to participate in our research firsthand.
While the rest of us are talking, Jessica likes to watch for bugs on the ground, or the Maasai cattle moving on the plains below our camp, or off into the distance to see anything moving in the hot sun. In fact, she alerted us to a herd of Grant's gazelle - a male, some females, and young - that were running in the distance. We're not sure what scared them. So far we've also seen a troop of baboons near one of our excavation sites. Typically, we also see and hear striped hyenas, jackels, the long-necked gerenuk (a kind of antelope), eland, giraffe, and ostrich. Some years, cheetah, leopard, and lions are also close by, usually in conflict with the Maasai who are very good at protecting their livestock from these predators.
This afternoon, Bernie went off to the Site Museum area to collect samples of diatoms, while I introduced Amanda and Lynn to the geology of the Olorgesailie region. The main set of geologic layers is known as the Olorgesailie Formation - and it's dated by a radioactive technique known as single-crystal argon dating to 1.2 million years old (the oldest layers in the region) to 493,000 years old. Beneath the oldest layers is the brown volcanic rock that erupted for a couple million years before, as the rift valley opened up in this region, before a lake basin began to form and lay down its characteristic white deposits. Laid on top of the 493,000-year layer are even younger sediments, which we've begun to explore the past few years. These deposits contain smaller and more refined stone tools, different from the large handaxes typical of what's called Acheulean technology. This more refined technology is called Middle Stone Age. It's the form of stone technology connected with the origin of our own species. We'll talk about this as our excavations of Middle Stone Age sites continue later this season.
For the time being, it's quite enough for Amanda and Lynn to learn about the Olorgesailie Formation, and how geologists have divided it into units, which are called members. These members are numbered from the bottom to the top - Member 1 is the oldest, Member 14 is the youngest. We saw all of the members as we walked from the Olorgesailie Field Museum back to camp. Each of the members has a distinctive rock type, which makes it easy to tell when and how the rocks were formed. After this brief geology lesson, we made it back to camp in time for chai, the 6pm tea break, and watched the sun set over the valley.