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：大的，频繁的流星撞击，地壳物质的形成和板块构造的启动。对早期地球的更大和更频繁的撞击将严重影响地球的大气，海洋和表面。这些撞击中的许多都蒸发了世界范围内几米深的海水，挖掘和蒸发了上地幔深处的岩石，并且发生的频率确保它们影响了生命的早期进化。35亿至24亿年前的10多次大撞击将地壳的不同部分挖掘到上地幔中，汽化的岩石形成了一个全球性的羽流，冷凝并沉积了这些物质作为球粒床沉积物。 这些矿床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，最重要的是缺乏任何明确的迹象表明海洋地壳在扩张中心形成，或大陆地壳创造稳定的平台。因此，对早期地球的研究通常局限于确定早期地壳形成、板块构造启动时间和大陆地壳提取的模型和代用品。这个CAREER研究项目将调查保存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成分，并确定与撞击有关的大气中的羽流过程。研究中的许多概念都是时空性的，如深时间、穿透性思维等。由于STEM表现与空间技能高度相关，与地质研究计划平行，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，并测试工具，以确定学习效果。指导本研究地质部分的首要科学问题是：（1）在35亿至24亿年前的许多大撞击现场，海洋地壳和上地幔的组成是什么？这能告诉我们关于前寒武纪地壳的什么？(2)撞击羽流是如何形成、凝结和结晶的？这些羽流对大气有什么影响？该CAREER项目将通过在澳大利亚皮尔巴拉克拉通和南非Kapvaal克拉通的综合实地工作方案、建模、岩相学、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描述海洋/地幔靶岩和撞击岩的特征，从而解决这些问题。这项研究将提供一个独特的见解，否则未保存的前寒武纪海洋地壳和地幔的组成，并将限制地球化学和机械过程中发生的影响羽流，以提高我们的理解的影响过程作为一个整体，这些影响的环境影响。研究计划的教学部分侧重于大规模3D概念的交流，这对学生来说是一场斗争，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，这个项目研究了手势在大教室中的效果，这对早期的本科学习者来说是一个特别有用的工具。此外，本研究还调查了使用3D打印技术来改善3D可视化和促进通用设计学习。

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.