CAREER: Developing novel biomarker proxies to constrain Neogene changes in African woody cover and paleoecological contexts of hominin evolution

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Today humans rely on grasses (e.g., corn, wheat, and rice) as a primary food source and for feeding livestock. This dependence on grasses has deep roots. Humans and their ancestors evolved in concert with grassland ecosystems in Africa over the past 7 million years. Despite the well-documented association between human evolution and grasslands, little is known about the origin of grasses in Africa, especially before 10 million years ago. When and how did grasses rise to ecological dominance? Lack of knowledge on this subject is largely due to the sparse plant fossil record. To understand how grasslands may have shaped the evolutionary trajectory of our species and other mammals, new, widely applicable approaches are needed to reconstruct ancient ecosystems. This project is developing new methods for reconstructing vegetation in past ecosystems using molecular plant fossils preserved in ancient sediments. Combining these approaches with existing isotopic methods, the researcher is reconstructing the rise of grasslands in East Africa over the past ~25 million years and exploring the relationships between climate, ecosystem, and evolutionary change. The results could produce new insights on the interconnectedness of climate, ecosystems and human evolution over geological timescales. A parallel objective throughout the project is to support students in their pursuit of STEM careers with an emphasis on increasing participation of underrepresented groups in the Earth sciences. The project includes intensive three-week field and lab courses for graduate students and postdocs from the US and African nations, lab-based research opportunities for undergraduate and New York City high school students, and support for a graduate student to conduct PhD research. African terrestrial ecosystems underwent revolutionary change in the Neogene. Sparse paleobotanical evidence suggests that denser forested ecosystems gave way to more open forests, woodlands, and perhaps nascent grasslands near the end of the early Miocene to the middle Miocene. This same period (~19 to 13 Ma) was marked by major changes in the primate and large mammal communities, yet the paleoecological context remains poorly known. By the late Miocene (10 Ma), carbon isotopic evidence shows that C4 grasslands began to spread. Despite the firm record of C4 grassland expansion beginning at 10 Ma, the role of ecological change in mammalian and human evolution through most of the Neogene has been insufficiently addressed. The Principal Investigator is developing organic geochemical approaches for reconstructing terrestrial ecosystem structure using modern ecosystems. This includes methods to estimate the fraction of woody cover from n-alkane molecular distributions and to measure grass abundance using PTMEs. Modern ecosystem research will also yield carbon and hydrogen isotope enrichment factors between biomarkers, bulk plant tissue, and soils. The researcher is applying these methods to terrestrial and marine sedimentary records from the Neogene Period in Africa to determine when and how grasslands became ecologically significant and how ecosystem change may have affected faunal and human evolution. The project will incorporate postdocs and graduate, undergraduate, and high school students into research, training, and field work. This includes developing a three-week paleoecology short course in Kenya for graduate students and postdocs from US institutions and African nations. The Principal Investigator is also providing research opportunities in his lab, built on a tiered mentoring program, for high school and undergraduate students from New York City. This program has high participation rates of students from underrepresented groups and serves as a pipeline for first-generation college students, many of whom ultimately major in STEM fields. One graduate student will be trained and supported by this project.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.