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2004 Field Season: Day 51

August 12, 2004

It's after dinner; everyone else has turned out their kerosene lamps and has gone to bed. I'll stay up a little longer, and since I have a tent large enough to fit a small table (along with my mattress and a couple cases of clothing and papers on the floor), I can write to you for a little while. I have one lamp on the table fueled by kerosene, the other a headlamp powered by batteries. They give plenty of light to see the keyboard inside my tent on this windy, moonless night. The sky's full of bright stars and the cloudy glow of our galaxy, the Milky Way. I stayed outside for a while to see if I could catch any of the meteor showers (the Perseid showers, I think they're called), which are prevalent around this time every year. About 15 minutes ago, I saw a really nice one - about a dozen meteors all at once, visible for a split second.

Sieving at Site 15

Our activities today involved final sieving of the sediment from Site 15, and covering Site CL1-1. From the photo above, you can tell that we had quite a large crew at Site 15. In the one below, we placed sediment and then plastic sheets over some remaining finds in the bottom of the CL1-1 excavation, protecting those finds for more work at the site next season.

Covering CL1-1

Since tomorrow is our last full day of excavation, let's sit back for a moment and sum up what we know about the handaxe-makers of Olorgesailie. What do we know about the lives of the Acheulean toolmakers?

We've hit some of the main points in earlier dispatches. We're sure they lived in small groups that moved around the landscapes of the southern Kenya rift valley. They probably didn't trade, or at least exchange large pieces of stone, with distant groups. Instead, they generally used very local rocks and carried a few pieces of stone from sources several tens of kilometers away into the Olorgesailie region.

These groups probably consisted of several families, but we don't have any direct evidence about the makeup of these families. The hominins were quite knowledgeable about the qualities of the rocks on which they depended for making tools. But rather than using different kinds of rock to produce different kinds of tools, they turned nearly every type of rock they found into handaxes, including rocks that are really pretty difficult to knap. Still, they used the very best quality rocks most often.

We have good evidence that the Olorgesailie hominins liked meat and marrow. Butchery of animals (including zebras, small antelopes, and elephants) left a strong mark in the archeological record of this region. This year, though, we may have finally found clues to the fact that the diet of these early humans included plants broken open or pulverized by using anvils and hammerstones. We think this occurred near water or wetlands, which we see evidence of at Site 15 and CL1-1. Later on, we'll test whether the anvils may have plant or animal proteins and residues preserved in the microscopic nooks and crannies of the rock surfaces.

Early humans made Acheulean tools for hundreds of thousands of years at Olorgesailie. While a handaxe is pretty simple equipment, these toolmakers were able to adapt to dramatic environmental change, which typified the rift valley of southern Kenya over the past million years or so. We now have a glimpse of the brow and braincase of one of these individuals. She or he was small in size. Was this individual powerful enough to make the largest handaxes, or were there also bigger individuals in the population? We don't know yet; only further discoveries will tell.

We know that they lived a lot in the highlands, since that's where all the source rocks were. If the high ground was home, it helps explain why early human fossils are so rare at Olorgesailie. In any case, they apparently knew that hanging out near water in the lowlands at night was not a very good life option. Frequent travel up and down the volcanic ridges connecting the highlands to the lake basin seems to explain why so many handaxes were left in these transition zones.

Olorgesailie keeps offering up new evidence - and its share of mysteries. We certainly wish to learn more about these early humans. Sometimes, it seems that the ancestors of this era, so long ago, are visible to our eyes for little more than a split second.