CAREER: Field Studies of Precambrian Impacts and Implications for the Early Crust and Environment

两个地质过程从根本上塑造了地球的早期历史：大而频繁的流星撞击，以及地壳物质的形成和板块构造的开始。对早期地球更大、更频繁的撞击会对大气、海洋和地球表面产生重大影响。许多这样的撞击蒸发了世界范围内几米深的海水，挖掘和蒸发了深至上地幔的岩石，并且发生的频率确保了它们影响了生命的早期进化。从35亿到24亿年前，10多次大的撞击将地壳的不同部分挖掘到上地幔中，蒸发的岩石形成了一个全球性的羽流，这些羽流将这些物质浓缩并沉积为球状床沉积物。这些沉积物今天仍保存在南非和澳大利亚。不幸的是，早期地球暴露的岩石记录仅限于小区域，并且主要由与现代地壳岩石不同的地壳岩石组成，最重要的是缺乏在扩张中心形成海洋地壳或大陆地壳形成稳定平台的任何明确迹象。因此，对早期地球的研究通常局限于模型和代用物，以确定早期地壳的形成、板块构造的起始时间和大陆地壳的提取。这个CAREER研究项目将调查保存下来的流星撞击沉积物的地球化学，以确定撞击地点的地壳和地幔组成，并确定与撞击有关的大气中的羽流过程。该研究的许多固有概念是时空的，如深度时间和渗透思维。由于STEM的表现与空间技能高度相关，与地质研究项目同时进行，本研究的教学部分侧重于开发工具，以提高本科生和研究生的3D思维，并测试这些工具以确定学习效果。指导这项研究的地质成分的首要科学问题是：(1)在35亿至24亿年前无数次大撞击的地点，海洋地壳和上地幔的成分是什么？这能告诉我们关于前寒武纪地壳的什么信息？(2)撞击羽流是如何形成、凝结和结晶的？它们对大气有什么影响？CAREER项目将通过对澳大利亚Pilbara克拉通和南非Kapvaal克拉通的综合实地考察、建模、岩石学、显微计算机断层扫描、扫描电子显微镜和其他地球化学分析来解决这些问题，以表征海洋/地幔目标岩石和撞击。这项研究将提供对未保存的前寒武纪海洋地壳和地幔组成的独特见解，并将约束发生在撞击羽流中的地球化学和机械过程，以提高我们对整个撞击过程和这些撞击的环境影响的理解。研究计划的教学部分侧重于大规模3D概念的交流，这对学生来说是一个难题，并帮助学生从课堂上典型的2D信息转向3D理解。由于仅用语言交流复杂的空间概念是困难的，本项目研究了手势在大教室中的作用，这对早期本科生学习者来说是一个特别有用的工具。此外，本研究探讨了利用3D打印技术来提高3D可视化和促进通用设计的学习。

Two geologic processes fundamentally shaped the early history of the Earth: large, frequent meteor impacts, and formation of crustal material and initiation of plate tectonics. The larger and more frequent impacts to the early Earth would have significantly affected the atmosphere, oceans and surface of the planet. Many of these impacts vaporized the top several meters of ocean water world-wide, excavated and vaporized rock as deep as the upper mantle, and occurred at a frequency that ensured that they influenced the early evolution of life. More than 10 large impacts from 3,500 to 2,400 million years ago excavated different parts of the crust into the upper mantle, and the vaporized rock formed a global plume that condensed and deposited this material as spherule bed deposits. These deposits are still preserved in South Africa and Australia today. Unfortunately, the early Earth's exposed rock record is limited to small regions and is largely comprised of crustal rocks that are dissimilar to modern crustal rocks, most importantly in lacking any clear indication of oceanic crust forming at spreading centers, or of continental crust creating stable platforms. Thus, studies of the early Earth are commonly limited to models and proxies to determine the early crust formation, timing of initiation of plate tectonics, and continental crust extraction. This CAREER research project will investigate the geochemistry of the preserved meteor impact deposits to determine crustal and mantle composition at the impact sites, and identify plume processes in the atmosphere associated with impact. Many of the concepts intrinsic to the research are spaciotemporal, such as deep time and penetrative thinking. Because STEM performance is highly linked to spatial skills, in parallel with the geological research program, the pedagogic component of this research focuses on developing tools to improve 3D thinking in undergraduate and graduate students, and testing the tools to determine the efficacy in learning.The overarching scientific questions that guide the geological component of this research are: (1) What is the ocean crust and upper mantle composition at the site of numerous large impacts from 3.5 to 2.4 billion years ago and what can that tell us about the Precambrian crust? (2) How do impact plumes form, condense, and crystallize and what effect do the plumes have on the atmosphere? This CAREER project will address these questions through an integrated program of fieldwork in the Pilbara craton of Australia and the Kapvaal craton of South Africa, modeling, petrography, micro-computed tomography, scanning electron microscopy, and other geochemical analyses to characterize the ocean/mantle target rock and impactites. This research will provide a unique insight into the composition of otherwise unpreserved Precambrian ocean crust and mantle, and will constrain the geochemical and mechanical processes that occur in impact plumes, to improve our understanding of the impact process as a whole and the environmental effects of these impacts. The pedagogic component of the research plan focuses on the communication of large-scale 3D concepts that are a struggle for students, and helps students move from 2D information typical of a classroom to 3D understanding. Because communicating complex spatial concepts is difficult with language alone, this project studies the effect of gesture in large classrooms, which is a particularly useful tool for early undergraduate learners. In addition, this research investigates the use of 3D printing technology to improve 3D visualization and promote universal design for learning.