TESTING HYPOTHESES FOR THE ROLE OF CLIMATE CHANGE IN HOMININ EVOLUTION USING THE GEOCHEMISTRY OF CARBONATES FROM THE EAST AFRICAN RIFT SYSTEM

A series of major hominin speciation events that took place in East Africa during the Pliocene-Pleistocene epochs have been linked to landscape evolution. Previous studies examining the role of climatic and environmental pressures on hominin evolution have used either discontinuous outcrops exposed proximal to, or marine sediments distal from, hominid fossil sites. These sediments have been used to develop stable carbon and oxygen isotope (¹³C, ¹⁸O) proxy-based reconstructions of paleoclimate, showing evidence for a series of changes including a transition from woodland to savannah-dominated environments. This work has prompted researchers to hypothesize that speciation events coincided with cooling of the African climate and local aridification during times of glacial intensification. It is speculated that local environmental pressures led to an increase in brain size, breakthroughs in stone technology, and the migration of Homo sapiens out of Africa. However, recent clumped isotope reconstructions from soil carbonates (Passey et al., 2010) have challenged this hypothesis, depicting relatively high and stable temperatures during the past 4 My. To find resolution between these competing hypotheses, we are examining paleosols and lake sediments near hominin fossil sites, including recently recovered drill cores that provide access to an unweathered and continuous archive of past environmental change. Isotopic data (δ¹³C, δ¹⁸O, and Δ₄₇) are used to constrain past changes in vegetation, hydrology, and temperature.