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，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影响将对大气、海洋和地球表面产生重大影响。其中许多撞击蒸发了世界范围内顶部几米深的海水，挖掘和蒸发了深达上地幔的岩石，并且发生的频率确保了它们影响了生命的早期进化。从3500年到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，蒸发的岩石形成了一股全球羽流，将这种物质浓缩并以球状床沉积的形式沉积。这些矿藏至今仍保存在南非和澳大利亚。不幸的是，早期地球裸露的岩石记录仅限于小区域，主要由不同于现代地壳岩石的地壳岩石组成，最重要的是缺乏任何明确的迹象表明洋壳在扩张中心形成，或大陆地壳形成稳定的平台。因此，对早期地球的研究通常局限于确定早期地壳形成、板块构造开始的时间和大陆地壳提取的模型和代理。这一职业研究项目将调查保存下来的陨石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。这项研究固有的许多概念都是时空的，比如深度时间和穿透性思维。由于STEM能力与空间技能高度相关，与地质学研究项目并行，这项研究的教学部分专注于开发工具来提高本科生和研究生的3D思维能力，并测试工具以确定学习效果。指导这项研究的地质学部分的首要科学问题是：(1)35亿至24亿年前多次大撞击地点的洋壳和上地幔成分是什么？这能告诉我们关于前寒武纪地壳的什么信息？(2)如何影响羽流的形成、浓缩和结晶，以及羽流对大气有什么影响？这个职业项目将通过在澳大利亚皮尔巴拉克拉通和南非卡普瓦尔克拉通的实地考察、建模、岩石学、微型计算机断层扫描、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岩。这项研究将对未保存下来的前寒武纪海洋地壳和地幔的组成提供独特的见解，并将限制撞击羽流中发生的地球化学和力学过程，以提高我们对撞击过程的整体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，这些概念对学生来说是一种挣扎，并帮助学生从课堂上典型的2D信息转移到3D理解。由于仅靠语言交流复杂的空间概念是困难的，该项目研究了手势在大教室中的效果，这对早期本科生学习者来说是一个特别有用的工具。此外，本研究还探讨了如何利用3D打印技术来提高3D可视化，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.