| 英文摘要: | 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. |