A 750,000-yr Leaf Wax Biomarker Record to Assess Environmental Change Across the Plio-Pleistocene Boundary in Tropical East Africa

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About three million years ago, the Arctic cooled dramatically, and northern hemisphere glaciers expanded and began to wax and wane in 41,000-year glacial cycles. Around the same time, parts of Africa became drier, and our human ancestors underwent a set of evolutionary shifts including the appearance of the genus Homo. Many studies have suggested that these changes are linked, wherein global cooling causes drying over Africa, which in turn triggers human evolutionary responses. This project will reconstruct environmental changes occurring in Africa between 3.3 and 2.5 million years ago to test the relationships between global climate transitions, African environmental change, and human evolutionary events. This research will provide an outstanding platform to train a diverse set of students and young researchers in interdisciplinary research in the Earth Sciences, including Brown University graduate students and undergraduate students from historically underrepresented groups. We will further develop new middle-school educational modules on environmental change and human evolution in collaboration with teachers from the Providence public schools.This project aims to develop new, high-resolution records of African environmental change through organic geochemical analyses of a recently recovered, exceptionally well-dated ~750,000-year-long drill core from the Baringo-Tugen-Barsemoi (BTB), in the Eastern Kenyan Rift that spans the Plio-Pleistocene boundary. We will analyze the hydrogen and carbon isotopic composition of terrestrial leaf wax biomarkers in this core to detect changes in rainfall and vegetation between 3.3 and 2.55 Ma. These data will be used to test the relationships between East African climate and vegetation and the onset and intensification of northern hemisphere glaciation, as well as other global and regional climate forcings. Our new data will be further compared to mammalian and hominin fossil datasets to test whether changes in the trend, variability, and rate of environmental change can be related to hominin evolutionary events. These state-of-the-art analyses will provide research training opportunities for a diverse set of graduate and undergraduate students and provide a framework to develop new middle-school educational modules on environmental change and human evolution that meet Next Generation Science Standards. Project results will refine our understanding of the connections between high and low latitude climate and the impacts of long-term vs. orbital-scale changes in global climate on African climate, ecosystems, and hominin evolution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.