The First Billion Years of the Geodynamo

地球发电机的第一个十亿年

• 批准号: 1656348
• 负责人: John Tarduno
• 金额: $ 45万
• 依托单位: University of Rochester
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-02-01 至 2021-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1656348&HistoricalAwards=false
• 关键词: First; Billion; Years; Geodynamo

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.

了解地球磁场何时开始对于了解地球核心、大气层和生命的演化非常重要。 PI 团队最近报告了对锆石（来自西澳大利亚杰克山的天然晶体）记录的地球古代磁场的首次测量，锆石是地球上已知最古老的材料，可以追溯到被称为冥古宙的时期。其中一些锆石含有磁性内含物，能够将磁场记录保存数十亿年。 3.3 至 42 亿年前的锆石数据记录的磁场强度与当今典型磁场的强度有所不同，仅为该值的 10% 左右。最早的冥宙地磁场可能是由地核中的化学沉淀（氧化镁）提供动力的。这种古老地球磁场的存在意味着早期大气演化受到发电机行为的调节。这些新的观察结果为继续工作提供了基础。研究人员希望完善地球发电机最初十亿年的历史，并通过现场和实验室项目测试其保真度。本科生和研究生培训以及国际合作以及实验室间比较和校准工作都融入了这些计划。了解地球发电机何时开始对于了解地球核心、大气和生命的演化非常重要。我们最近报告了对来自杰克山砾岩（西澳大利亚）的带有磁性包裹体的太古宙到冥宙锆石的首次古强度测量，以重建早期的地球发电机历史。 3.3 至 42 亿年前的锆石数据记录了磁场变化范围为近期赤道磁场强度的 ¡1.0 至 0.12 倍。冥宙地磁场可能是由地核中氧化镁的化学沉淀提供动力的。陆地N同位素证据支持在晚期重轰炸之前存在陆地磁场，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努力完善地球发电机最初十亿年的历史并测试其保真度奠定了基础。我们概述了构成我们工作计划基础的 8 项任务： 1. 太太古代和冥宙锆石的岩石磁性、各向异性研究和完整的泰利尔-科分析； 2. 锆石中磁性包裹体的成像； 3. 对西澳大利亚新地点的锆石进行分析； 4. 对津巴布韦新地点的锆石进行分析； 5. 再热情景的新测试，包括锂分区研究； 6. 实验室间和仪器比较以及样本分配； 7. 对早期地球的地地-太阳相互作用的研究和 8. 根据我们的发现对地球深层内部的热演化进行研究。最终，我们的目标是广泛定义月球形成对古太古代时代的巨大撞击之后的第一个十亿年的地球发电机历史，并评估这一记录对大气、地幔和地核演化的影响。拟议的工作将为研究生和本科生提供支持，他们将通过实地研究和实验室培训获得宝贵的技能。我们的本科教育计划的突出方面及其与我们研究的结合包括：作为本科生暑期研究计划的一部分，在西澳大利亚和津巴布韦进行采样实地考察，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。拟议的工作将有助于博士学位。和硕士。论文。我们还向罗切斯特大学古地磁实验室提出了一个访问科学家计划，为罗切斯特大学过去二十年来开发的单硅酸盐晶体古地磁分析方法提供社区指导的机会。

项目成果

Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo

• DOI: 10.1073/pnas.1916553117
• 发表时间: 2020-01
• 期刊: Proceedings of the National Academy of Sciences of the United States of America
• 影响因子: 11.1
• 作者: J. Tarduno;R. Cottrell;R. Bono;H. Oda;W. Davis;M. Fayek;O. V. Erve;F. Nimmo;Wentao Huang;E. Thern;S. Fearn;G. Mitra;A. V. Smirnov;E. Blackman

Cluster analysis on a sphere: Application to magnetizations from metasediments of the Jack Hills, Western Australia

• DOI: 10.1016/j.epsl.2017.12.007
• 发表时间: 2018-02-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Bono, Richard K.;Tarduno, John A.;Cottrell, Rory D.
• 通讯作者: Cottrell, Rory D.