The ultimate objective of the program of research on the chronology of the Middle Stone Age (MSA) and Early Later Stone Age (LSA) in the southern and central Rift Valley of Kenya is to document the emergence of modern human behavior in East Africa. Archaeological evidence suggests that behavioral innovations that characterize modern human behavior occurred during the later MSA and early LSA in eastern and southern Africa, at an earlier date than in other parts of Africa and the Old World.
Accurate chronometric dates for the MSA and the transition to the LSA will contribute to testing the hypothesis of an East African origin for modern human behavior.
The primary objective of the 1999 field season in the southern Rift Valley was to excavate MSA and Early LSA archaeological occurrences that contain volcanic tephra stratified for Single Crystal Laser Fusion (SCLF) 40Ar/39Ar dating. One paleontological and four archaeological sites were excavated. The paleontological site, apparently a fossil hyena den, contains cut-marked bones.
Two sites have typical MSA occurrences characterized by lithic assemblages with radial cores and faceted platform flakes, made predominantly on locally available lavas. Two sites have artifact occurrences with diagnostic features of both the MSA and LSA, including backed microliths and elongated triangular flakes with faceted platforms from levallois cores, predominantly made on obsidian. These sites have excellent faunal preservation. Twelve stratified tephra were sampled from these five sites. Samples from the four archaeological sites have been submitted for dating
and chemical fingerprinting by Al Deino at the Berkeley Geochronology Center. Three sites also contained ostrich eggshell, permitting dating by amino acid racemization by Gifford Miller.
Three hydroelectric dams will be constructed by KenGen in the heart of the survey area, and river discharge will be increased by diverting a major tributary of the Mara River. Construction will begin in 2001, and be completed by 2006. Many important fossil and archaeological localities will be inundated, so intensive survey and excavations must be undertaken in a timely fashion.