The First Billion Years of the Geodynamo

了解地球磁场何时开始，对于理解地核、大气和地球生命的演化非常重要。PI团队最近报告了对地球古代磁场的首次测量，记录在锆石中-来自西澳大利亚州杰克山的天然晶体，是地球上最古老的已知材料，可以追溯到被称为Hadean的时间段。其中一些锆石含有磁性包裹体，能够保存数十亿年的磁场记录。来自33亿至42亿年前的锆石的数据记录了磁场的强度，这些磁场的强度与现代磁场的典型强度不同，只有该值的10%左右。最早的冥古宙地磁场可能是由核心中的化学沉淀（MgO）提供动力的。这个古老的地球磁场的存在意味着早期的大气演化是由发电机行为调节的。这些新的观察结果为继续开展工作提供了基础。研究人员希望通过实地和实验室项目来完善地球发电机最初10亿年的历史，并测试其真实性。本科生和研究生的培训被整合到这些项目中，国际合作和实验室间的比较和校准工作也是如此。了解地球发电机何时开始对于理解地核、大气和地球上生命的演变非常重要。我们最近报道的第一个古强度测量太古宙Hadean锆石轴承磁性包裹体从杰克山砾岩（西澳大利亚州）重建早期的地质发电机的历史。来自33亿至42亿年前的锆石的数据记录了磁场变化，其变化范围是现代赤道磁场强度的1.0倍至0.12倍。冥古宙地磁场可能是由核心中MgO的化学沉淀提供动力的。地球N同位素证据支持在晚期重轰炸之前存在地球磁场，这意味着地球和火星的早期大气演化受到发电机行为的调节。这些新的观测结果为我们继续完善地球发电机最初10亿年的历史并测试其真实性提供了基础。我们概述了构成我们工作计划基础的8项任务：1.始新世和冥古宙锆石的岩石磁性、各向异性研究和完整的Thellier-Coe分析; 2.锆石中磁性包裹体的成像; 3.西澳大利亚新地点的锆石分析; 4.津巴布韦新地点的锆石分析; 5.重新加热情景的新测试，包括Li分区的研究; 6.实验室间和仪器间比较以及样本分布; 7.早期地球和8的地日相互作用研究。利用我们的发现对地球深部的热演化进行研究。最终，我们的目标是广泛地定义地球发电机的第一个十亿年的历史，从月球形成的巨大撞击到古太古代，并评估这一记录对大气，地幔和地核演化的影响。拟议的工作将支持研究生和本科生，他们将通过实地研究和实验室的培训获得宝贵的技能。我们的本科教育计划的突出方面，并融入我们的研究，包括我。在西澳大利亚州和津巴布韦进行实地考察取样，作为本科生暑期研究计划的一部分，涉及岩石磁性，古地磁和电子显微镜分析; ii.本科研究课程导致高级论文。建议的工作将有助于博士学位。和史密斯论文我们还提出了一个访问科学家计划的罗切斯特大学古地磁实验室，提供了机会，为社区的指导方法的硅酸盐单晶古地磁分析在罗切斯特在过去的二十年。

Knowing when Earth's magnetic field began is important for understanding the evolution of the core, atmosphere and life on Earth. The PI team has recently reported the first measurements of Earth's ancient magnetic field as recorded in zircons- natural crystals from the Jack Hills of Western Australia that are the oldest known materials on Earth, dating to a time period known as the Hadean. Some of these zircons host magnetic inclusions capable of preserving magnetic field records for billions of years. Data from zircons between 3.3 and 4.2 billion-years-old record magnetic fields that vary in strength from those typical of the present-day field, to only about 10% of that value. The earliest Hadean geomagnetic field may have been powered by chemical precipitation (of MgO) in the core. The existence of this ancient terrestrial magnetic field implies that early atmospheric evolution was regulated by dynamo behavior. These new observations provide the basis for continued work. The investigators hope to refine the history of the first billion years of the geodynamo and to test its fidelity through field and laboratory based programs. Undergraduate and graduate student training is integrated into these programs, as is international collaboration and inter-laboratory comparison and calibration efforts.Knowing when the geodynamo started is important for understanding the evolution of the core, atmosphere and life on Earth. We have recently reported the first paleointensity measurements of Archean to Hadean zircons bearing magnetic inclusions from the Jack Hills conglomerate (Western Australia) to reconstruct the early geodynamo history. Data from zircons between 3.3 and 4.2 billion-years-old record magnetic fields varying between ¡­1.0 and 0.12 times recent equatorial field strengths. A Hadean geomagnetic field may have been powered by chemical precipitation of MgO in the core. The existence of a terrestrial magnetic field prior to the Late Heavy Bombardment is supported by terrestrial N isotopic evidence and implies that early atmospheric evolution on both Earth and Mars was regulated by dynamo behavior. These new observations provide the basis for our continued work to refine the history of the first billion years of the geodynamo and to test its fidelity.We outline 8 tasks that form the basis of our work plan: 1. Rock magnetism, anisotropy studies and full Thellier-Coe analyses of Eoarchean and Hadean zircons; 2. Imaging of magnetic inclusions in zircons; 3. Analyses of zircons from new sites in Western Australia; 4. Analyses of zircons from new sites in Zimbabwe; 5. New tests of re-heating scenarios, including studies of Li zoning; 6. Inter- lab and instrument comparisons and sample distribution; 7. Studies of terrestrial-solar interactions for the early Earth and 8. Studies of the thermal evolution of Earth¡¯s deep interior informed by our findings. Ultimately, our goal is to broadly define the first billion years of geodynamo history, after the Lunar-forming giant impact to Paleoarchean times, and to evaluate the implications of this record for the evolution of the atmosphere, mantle and core.The proposed work will support graduate students and undergraduates, who will acquire valuable skills through training in field studies and in the laboratory. Salient aspects of our undergraduate education plans, and its integration into our research, include i. field excursions for sampling in Western Australia and Zimbabwe as part of an undergraduate summer research program involving rock magnetic, paleomagnetic and electron microscope analyses and ii. undergraduate research courses leading to Senior theses. The work proposed will contribute to Ph.D. and M.S. theses. We also propose a visiting scientist program to the University of Rochester paleomagnetic laboratories, providing the opportunityfor community instruction on methods of single silicate crystal paleomagnetic analyses developed at Rochester over the last twenty years.