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

大约300万年前，北极急剧降温，北半球冰川膨胀，开始以41000年的冰川周期消长。大约在同一时间，非洲部分地区变得更加干旱，我们的人类祖先经历了一系列进化转变，包括人属的出现。许多研究表明，这些变化是相互关联的，其中全球变冷导致非洲上空干旱，进而引发人类进化反应。该项目将重建330万至250万年前非洲发生的环境变化，以测试全球气候变化、非洲环境变化和人类进化事件之间的关系。这项研究将提供一个杰出的平台，培养一批在地球科学跨学科研究方面的学生和年轻研究人员，包括布朗大学的研究生和来自历史上代表性不足的群体的本科生。我们将与普罗维登斯公立学校的教师合作，进一步开发关于环境变化和人类进化的新的中学教育模块。该项目旨在通过对最近从横跨更新世-更新世边界的肯尼亚东部裂谷巴林戈-图根-巴尔塞莫伊(BTB)发现的、特别好的~75万年长的钻芯进行有机地球化学分析，开发新的、高分辨率的非洲环境变化记录。我们将分析该岩心陆相叶蜡生物标志物的氢和碳同位素组成，以探测3.3 Ma至2.55 Ma期间降雨量和植被的变化。这些数据将被用来测试东非气候和植被与北半球冰川开始和加剧之间的关系，以及其他全球和区域气候压力。我们的新数据将进一步与哺乳动物和人类化石数据集进行比较，以测试环境变化的趋势、变异性和速度的变化是否与人类进化事件有关。这些最先进的分析将为不同的研究生和本科生提供研究培训机会，并提供一个框架，以开发符合下一代科学标准的关于环境变化和人类进化的新的中学教育模块。项目成果将加深我们对高纬度和低纬度气候之间的联系以及全球气候长期变化和轨道尺度变化对非洲气候、生态系统和人类进化的影响的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.