Day 38 (August 2, 2011): Rahab and the Phytoliths

August 2, 2011

portrait of Rahab Kinyanjui Paleobotanist, Rahab Kinyanjui We’re in our last few days of the field season, but research is still going full speed ahead. Joining us for these last few days is our Kenyan friend and paleobotanist, Ms. Rahab Kinyanjui.

Rahab was born and raised in Nakuru, Kenya. She attended primary school in Nakuru and high school in Thika.  Her science interests soared at the Kenyan Polytechnic, where she did a dissertation studying the archeology, pollen analysis, and reconstruction of a site in Nakuru called Hyrax Hill. After graduating from the Polytechnic with her 3-year diploma, Rahab began work at the National Museums of Kenya (NMK) studying palynology and paleobotany. It was here where we crossed paths for the first time, in 2001. 

I worked with a colleague at the NMK for several years in an effort to identify fossil pollen grains, from ancient vegetation, in the sediments at Olorgesailie.  Those efforts never succeeded, as the sediments were simply not a good environment for preserving pollen.  I was looking for a different approach in understanding what plant species and vegetation existed in the past. Rahab joined us the summer of 2001, where we undertook another trial in getting pollen out of the old lake sediments. Again, the attempt failed because pollen had not been adequately preserved. 

Yet by then, Rahab had begun to explore an alternative indicator of ancient plants besides pollen; the alternative is called phytolith analysis. Phytoliths, which means ‘plant stones’, are minute particles, made mostly of silica, that form in leaves and stems when the plant grows. They remain in the surrounding sediment after the plant dies. The value of studying phytoliths is that they retain the chemistry of the plant in which they formed. Unlike pollen, phytoliths can indicate whether a landscape consisted of woody C3 plants, which may prevail in a moist environment, or of C4 grasses in a more arid environment (Day 28).  The shapes of the stones can also indicate the identity of the plants that formed them. 

When Rahab first collected sediment samples at Olorgesailie beginning in 2001, her study began to yield results!

Young woman in blue jeans, dark shirt and a hat sits high above on the top step of the geologic trench holding geological hammer Rahab Kinyanjui collects sediment samples in the field. Back in the lab, she analyzes the sediment microscopically in search of the plant phytoliths. Rahab continued this research and has spent her last few years at the University of Cape Town, South Africa, where she has completed a masters dissertation comparing phytoliths through a series of sedimentary layers at Olorgesailie. The phytoliths show evidence of fluctuating conditions of climate and vegetation; for example, a time when the climate became wetter and cooler, with increased C3 plants, was followed by aridity and an increase in grasses. In just a few weeks, she will be finished with her Masters Degree! Her research shows the value and potential of phytolith studies as a novel way of learning about past environmental change. 

Of course, Rahab’s ambition does not end there. She has joined us again this summer to collect more samples, and she aspires to a PhD. Her dissertation research will be focused on Olorgesailie and she will analyze the phytoliths that we expect will be found in a deep core we will drill from the ground.  This is work we plan to conduct at Olorgesailie next year. This is all very impressive considering the fact that Rahab is married with two young daughters, age ten and five. In the future she hopes to be a lecturer/researcher at a university, and she intends to stay in Kenya.