July 17, 2011
It’s been a brief but excellent visit. The Homa Peninsula is a place of spectacular views of Lake Victoria, some of them right next to equally spectacular archeological sites. The photo to the left shows an example from earlier today.
Today our excursions took us across nearly 6 million years of time. We eagerly returned to Kanam West, where we began our brief investigations on the Homa Peninsula four days ago. For a couple hours, we explored the layers where in previous years we found fossils of animal species that lived around 6 million years ago, based on dates at other fossil sites in East Africa. Several layers of gray ash were obvious on the eroded slopes, and we collected bags of the ancient ash to date through a precise method called single-crystal argon dating. The technique allows you to identify and isolate populations of volcanic particles, or crystals, which were erupted at different times. Ash layers may, in fact, combine crystals from several past eruptions. Yet by dating each crystal (lasers are critical to the method!), you can identify the youngest set of crystals in each ash, compared to the ash layer below it in the sequence. In this way, the older contaminant crystals in each layer can be eliminated. So you’re left with the youngest set crystals, and mathematical analysis can then provide precise dates for each volcanic ash layer. One of our group from China, Dr. He Huaiyu, is an expert in the method, which is now practiced by geological dating specialists around the world.
During our travels around the Peninsula today, we discussed the age of Lake Victoria. Despite its vast size, the current lake is only about 200,000 to 700,000 years old. The older sediments we’ve been exploring on the Peninsula show no evidence of a large lake. It’s pretty clear that earthquake activity and faulting within the past 700,000 years must have created the enormous shallow basin that filled with what we know as Lake Victoria. The evolution of fish in the lake, a huge number of species known as cichlid fish (pronounced sick-lid), all occurred within a few hundred thousand years, based on genetic comparisons. So the data from both geology and genetics are consistent with each regarding the relatively recent age of the lake.
Finally, we ended up at a site called Luanda, on the southern part of the Peninsula. It made me think of Olorgesailie and the excavations there. That’s because we found a lot of Middle Stone Age artifacts at Luanda, some of them similar to what our team has been finding at BOK-2 excavation. This technology, associated with the origin of our own species, spread across the Rift Valley and throughout Africa, hinting at the talent of Homo sapiens, eventually, to spread around the world.