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

今天，人类依靠禾草（如玉米、小麦和水稻）作为主要食物来源和饲养牲畜。这种对草的依赖有很深的根源。在过去的700万年里，人类和他们的祖先与非洲的草原生态系统一起进化。尽管人类进化与草原之间存在着充分的联系，但人们对非洲草的起源知之甚少，尤其是在1000万年前。草是什么时候以及如何获得生态优势的？这方面的知识缺乏主要是由于植物化石记录的稀少。为了理解草原如何塑造了人类和其他哺乳动物的进化轨迹，我们需要新的、广泛适用的方法来重建古代生态系统。该项目正在开发利用保存在古代沉积物中的分子植物化石重建过去生态系统植被的新方法。将这些方法与现有的同位素方法相结合，研究人员正在重建过去~ 2500万年东非草原的兴起，并探索气候、生态系统和进化变化之间的关系。这些结果可能会对气候、生态系统和人类进化在地质时间尺度上的相互联系产生新的见解。整个项目的另一个平行目标是支持学生追求STEM职业，重点是增加代表性不足的群体在地球科学领域的参与。该项目包括为来自美国和非洲国家的研究生和博士后提供为期三周的强化实地和实验室课程，为本科生和纽约市高中生提供实验室研究机会，并为研究生进行博士研究提供支持。非洲陆地生态系统在新近纪经历了革命性的变化。稀疏的古植物学证据表明，在中新世早期到中新世中期，密集的森林生态系统让位给了更开阔的森林、林地，或许还有新生的草原。在同一时期（~19 ~ 13 Ma），灵长类动物和大型哺乳动物群落发生了重大变化，但其古生态背景尚不清楚。到晚中新世（10 Ma），碳同位素证据表明C4草地开始扩张。尽管C4草地扩张的确切记录始于10 Ma，但在大部分新近纪，生态变化在哺乳动物和人类进化中的作用尚未得到充分的解决。首席研究员正在开发利用现代生态系统重建陆地生态系统结构的有机地球化学方法。这包括估算正构烷烃分子分布中木质覆盖的比例，以及使用PTMEs测量草丰度的方法。现代生态系统研究也将在生物标记物、大块植物组织和土壤之间产生碳和氢同位素富集因子。该研究人员正在将这些方法应用于非洲新近纪的陆地和海洋沉积记录，以确定草原何时以及如何变得具有生态意义，以及生态系统变化如何影响动物和人类进化。该项目将包括博士后、研究生、本科生和高中生参与研究、培训和实地工作。这包括在肯尼亚为来自美国机构和非洲国家的研究生和博士后开设一个为期三周的古生态学短期课程。首席研究员还在他的实验室里为来自纽约市的高中生和本科生提供了一个分层指导计划的研究机会。这个项目的学生参与率很高，来自代表性不足的群体，是第一代大学生的管道，其中许多人最终主修STEM领域。该项目将培训和支持一名研究生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.