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.

了解地球磁场是何时开始的，对于了解地球核心、大气和生命的演化非常重要。Pi团队最近报告了首次测量到的地球古代磁场的记录-锆石-来自西澳大利亚杰克山的天然晶体，是地球上已知的最古老的物质，可以追溯到被称为Hadean的时期。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，这些磁场的强度与当今磁场的典型值不同，只有这个值的10%左右。最早的哈迪亚地磁场可能是由核心中的化学沉淀(氧化镁)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的行为决定的。这些新的观察结果为继续开展工作奠定了基础。研究人员希望提炼出地球发电机最初10亿年的历史，并通过基于现场和实验室的项目来测试它的保真度。本科生和研究生培训被纳入这些项目，国际合作以及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启动对于了解地球核心、大气和生命的演化非常重要。我们最近首次报道了来自杰克山砾岩(西澳大利亚)的太古宙至赫甸期含磁性包裹体的锆石的古强度测量，以重建早期地球发电机的历史。来自3.3到42亿年前的锆石的数据记录的磁场变化在1.0到0.12倍于最近的赤道磁场强度。Hadean地磁场可能是由地核中氧化镁的化学沉淀提供动力的。陆地氮同位素证据支持在晚期强烈轰击之前存在地球磁场，并暗示地球和火星上的早期大气演化都受到发电机行为的调节。这些新的观察结果为我们继续完善地球发电机最初10亿年的历史和测试其保真度提供了基础。我们概述了构成我们工作计划基础的8项任务：1.岩石磁性、各向异性研究和对早太古代和哈迪期锆石的全面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分带研究；6.实验室间和仪器间的比较和样品分布；7.早期地球的地-日相互作用研究8.地球内部热演化的研究S由我们的发现启发。最终，我们的目标是广泛地定义地球发电机历史的第一个10亿年，在月球形成对古太古时代的巨大撞击之后，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，他们将通过野外研究和实验室培训获得宝贵的技能。我们本科教育计划的突出方面及其与我们研究的整合，包括：1.作为本科暑期研究项目的一部分，在西澳大利亚和津巴布韦进行采样的实地考察；2.岩石磁学、古地磁和电子显微镜分析。本科生研究课程通向高级论文。建议的工作将对博士和硕士论文做出贡献。我们还向罗切斯特大学的古地磁实验室提出了一个访问科学家计划，为罗切斯特大学在过去20年里开发的单硅酸盐晶体古地磁分析方法的社区指导提供了机会。

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.