EAR-PF: Investigating Redox-Related Preservation of Organic-Walled Microfossils in Proterozoic Shales: a Multi-Scale Approach.

克里斯蒂娜·沃尔茨博士被授予NSF EAR博士后奖学金，在斯坦福大学开展研究和教育计划。在大约5.5亿年前动物广泛出现之前，地球上的生命几乎完全是微小的。真核生物--包括动物、植物和各种单细胞生物在内的生命领域--首次出现在化石记录中是在大约1.65亿年前，当时微观的有机结构被压缩在细粒岩石中。尽管他们的化石记录记录了随着时间的推移多样性的大规模变化，但它也可能受到控制石化的环境条件变化的影响。特别是，氧的存在被认为会增加有机物的降解，但氧对早期真核化石记录质量的影响还没有得到全面的研究。该项目的目标是探索埋葬环境中氧气的存在如何影响微化石组合的保存质量。通过了解微化石保存和氧气之间的关系，这个项目将评估氧浓度波动的某些时间间隔是否偏离了我们目前对早期真核生物进化的理解。该项目还将开发教学模块，将本科生与当前的研究主题联系起来，使用一个大型的开放访问的地球化学数据库(可通过沉积地球化学和古环境项目获得)。这些教学单元将使学生接触地球科学的应用，这增加了学生的参与度，并使他们掌握数据管理技能，以支持他们继续参与科学。长期以来，人们一直认为，局部海洋缺氧是有机遗骸石化所必需的。尽管这种关系在软组织动物化石的显生界记录中得到了很好的记录，但还不清楚同样的条件是否适用于元古界有机壁微化石的记录。这里，微化石组合的保存质量将与几个氧化还原指标--包括铁的形态以及铀和钼的丰度--进行比较，这些指标是从一套跨越中、晚元古代的页岩样品中测量出来的。由于氧化还原条件可能会在短时间间隔内发生显著变化，因此将使用基于同步加速器的X射线光谱分析在选定样品上以超高分辨率测量氧化还原替代物(包括铁物种)。通过量化化石保存与古氧化还原条件之间的关系，该项目为在元古界化石记录中检测保存潜力的大范围变化奠定了基础。例如，化石记录中首次出现真核生物的时间(约1650 Ma)比分子时钟估计和第一批真核化石的复杂性预测的要晚得多。有可能此时真核生物的出现标志着更有利的保存条件的开始。此外，该项目还开发了旨在让不同的本科生社区参与地球科学研究的教学模块。实验室模块将开发与管理和分析大型数据集相关的技能，这是本科生群体中必要但尚未开发的技能。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。

Dr. Christina Woltz has been awarded an NSF EAR Postdoctoral Fellowship to carry out research and education plans at Stanford University. Before the widespread appearance of animals around 550 million years ago, life on Earth was almost entirely microscopic. Eukaryotes—the domain of life that includes animals, plants, and a great diversity of single-celled organisms—first appear in the fossil record around 1650 million years ago as microscopic organic structures compressed in fine-grained rock. Although their fossil record documents large-scale changes in diversity through time, it can also be influenced by changes in the environmental conditions that control fossilization. In particular, the presence of oxygen is thought to increase the degradation of organic matter, but the effects of oxygen on the quality of the early eukaryotic fossil record have not been examined comprehensively. The goal of this project is to explore how the presence of oxygen in the burial environment might have influenced the preservational quality of microfossil assemblages. By understanding the relationship between microfossil preservation and oxygen, this project will assess if certain time intervals of fluctuating oxygen concentrations have biased our current understanding of early eukaryotic evolution. This project will also develop teaching modules that connect undergraduate students to current research topics using a large open-access geochemistry database (available through the Sedimentary Geochemistry and Paleoenvironments Project). These teaching modules will expose students to applications of Earth science, which increases student engagement, and equips them with skills in data management to support their continued involvement in science. It is a long-held assumption that local ocean anoxia is necessary for the fossilization of organic remains. Although this relationship is well-documented in the Phanerozoic record of soft-tissue animal fossils, it is unclear if the same conditions apply to the record of Proterozoic organic-walled microfossils. Here, the preservational quality of microfossil assemblages will be compared to several redox proxies—including iron speciation, and uranium and molybdenum abundances—measured from a suite of shale samples that span mid to late Proterozoic time. Since redox conditions can vary significantly over short time intervals, redox proxies (including iron species) will be measured at ultra-high resolution on select samples using synchrotron-based x-ray spectroscopy. By quantifying the relationship between fossil preservation and paleoredox conditions, this project lays the groundwork for detecting largescale changes in preservation potential within the Proterozoic fossil record. For example, the first appearance of eukaryotes in the fossil record (around 1650 Ma) occurs much later than is predicted by molecular clock estimates and the complexity of the first eukaryotic fossils. It is possible that the appearance of eukaryotes at this time marks the onset of more favorable preservational conditions. Additionally, this project develops teaching modules aimed towards engaging a diverse undergraduate community in Earth science research. Laboratory modules will develop skills related to the management and analysis of large datasets, which are necessary yet underdeveloped skills in the undergraduate population.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.