The First Billion Years of the Geodynamo

地球发电机的第一个十亿年

• 批准号: 2051550
• 负责人: John Tarduno
• 金额: $ 46.5万
• 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: 2021
• 资助国家: 美国
• 起止时间: 2021-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2051550&HistoricalAwards=false
• 关键词: First; Billion; Years; Geodynamo

Earth's magnetic field, generated in the liquid iron core, shields the atmosphere from particles streaming from the Sun, known as the “solar wind". Without this shield, the atmosphere would have been eroded, and water would have been lost, especially when Earth was young and solar winds were intense. Hence, knowledge of Earth's earliest magnetic field can provide unique insight into the evolution of our planet's core and atmosphere. Because water is essential to life as we know it, this knowledge also bears on the origin of Earth's habitability. The only known material that can accurately record this early magnetic history is the mineral zircon, now found as tiny grains in younger sedimentary rocks. Some of these zircons are remarkable because they contain even smaller inclusions that can preserve signals of the ancient magnetic field from billions of years ago. But because these zircons are so small - only a few times thicker than a human hair - the measurement of their magnetism is extremely challenging. The investigators have developed and applied new techniques to characterize the nature of magnetic inclusions in zircons and to retrieve their magnetic signals, using a host of highly sensitive instruments. Their measurements indicate the presence of a magnetic field at least 4.2 billion years ago. These data indicate atmospheric shielding was in place. They also place constraints on the physical conditions in the core that resulted in the generation of a strong magnetic field. The investigators will fill gaps in the magnetic field history, generating data from new zircon localities in Western Australia, India and southern Africa. They will work with a team of international collaborators spanning 6 countries in multidisciplinary laboratory studies. The team will then use these new data to test the fidelity of the magnetic history, and to further explore the implications for magnetic shielding and Earth evolution. The work will support graduate and undergraduate students who will receive broad training in the field and in multidisciplinary analyses, and will include outreach to Rochester secondary schools through programs hosted for instructors and students.Knowledge of the earliest history of the geomagnetic field can provide key insight into our understanding of the evolution of the core, atmosphere and Earth's habitability. The only known materials that can be accurately dated and that are able to record this history on the multi-hundred-of-million-year time scales required to advance our understanding of these fundamental issues of Earth evolution are Eoarchean to Hadean zircons bearing minute magnetic inclusions that are now found in younger sedimentary units. However, the magnetic measurement of zircons, and interrogations of their magnetizations to determine if they preserve primary signals, are formidable technical challenges requiring a multidisciplinary approach. The investigators have recently presented new paleomagnetic, electron microscope, geochemical, and paleointensity data that indicate the presence of primary magnetite inclusions in select zircons from the Jack Hills of Western Australia. These new data further support that select Jack Hills zircons record primary magnetic signals of the geodynamo, with a record extending back in time to ~4.2 billion years ago. These analyses thus indicate that shielding of the atmosphere by the magnetosphere was in place very early in Earth history. The new analyses also suggest a strong magnetic field in the Late Hadean at ~4 billion years ago which could be a signal that chemical precipitation in the core was powering the geodynamo. The team will use a paleomagnetic approach to further test and fill gaps in the paleointensity record building on recent discoveries of Eoarchean to Hadean detrital zircons at other global sites. Specifically, they will generate records spanning hundreds-of-millions of years from new localities in Western Australia, India and southern Africa. They will work with a team of international collaborators spanning 6 countries in multidisciplinary laboratory studies [including light and scanning electron microscopy, focused ion beam slice and view and lift-outs, transmission electron microscopy, magneto-optical Kerr effect measurements, ultra-sensitive 3-component direct current superconducting quantum interference device (SQUID) magnetometry, scanning SQUID microscope magnetometry, sensitive high-resolution ion microprobe (SHRIMP) analyses, and secondary-ion mass spectrometry (SIMS)]. The team will use these new data to test the internal fidelity of each record, test consistency between records, and further explore the implications for planetary magnetic shielding and chemical evolution of the core. The work will support graduate and undergraduate students who will receive broad training in multidisciplinary analyses. The work will contribute to Ph.D. and M.S. theses. The investigators will continue outreach to Rochester secondary schools by hosting programs for instructors and students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球的磁场是在液态铁芯中产生的，它屏蔽了从太阳流出的颗粒（称为“太阳风”）的颗粒。没有这种盾牌，大气就会发出，水会流失，尤其是当地球年轻而太阳风强烈的时候。因此，对地球最早的磁场的了解可以为我们星球的核心和气氛的演变提供独特的见解。由于水对我们所知的生命至关重要，因此这些知识也依赖于地球可居住的起源。唯一可以准确记录此早期磁历史的唯一已知材料是矿物锆石，现在被发现为年轻沉积岩中的微小谷物。这些锆石中的一些是显着的，因为它们包含甚至可以保留数十亿年前古代磁场信号的较小夹杂物。但是，由于这些锆石太小了 - 仅比人的头发厚几次 - 磁性的测量极具挑战性。研究人员已经开发并应用了新技术来表征锆石中磁性夹杂物的性质，并使用许多高度敏感的仪器来检索其磁信号。它们的测量表明至少42亿年前存在磁场。这些数据表明大气屏蔽已经到位。他们还对核心的物理条件放置了限制，从而导致了强磁场的产生。研究人员将填补磁场历史上的空白，从而产生来自西澳大利亚，印度和南非新锆石地区的数据。他们将与跨越6个国家 /地区的国际合作伙伴团队合作。然后，团队将使用这些新数据来测试磁历史的忠诚度，并进一步探索对磁屏蔽和地球演化的影响。这项工作将支持将在该领域和多学科分析中接受广泛培训的毕业生和本科生，并通过为教师和学生提供的计划包括向罗切斯特中学的宣传。了解地磁领域的最早历史可以为我们对我们对核心，大气层和地球的发展的理解提供关键的见解。唯一可以准确过时的材料能够在促进我们对这些地球进化的这些基本问题的理解所需的数百万年度尺度上记录这一历史的材料，这是对携带较小磁性包含物的Hadean Zircons的eoarchian，这些磁性含量现在在年轻的沉积单元中发现。但是，锆石的磁性测量以及对它们是否保留主要信号的磁化的询问是需要多学科方法的正式技术挑战。研究者最近介绍了新的古磁，电子显微镜，地球化学和古意志数据，这些数据表明来自西澳大利亚州杰克山的精选锆石中存在原代磁铁矿夹杂物。这些新数据进一步支持，选择杰克山锆石记录了地​​球上的主要磁信号，并且记录及时延伸至约42亿年前。因此，这些分析表明，磁层对大气的屏蔽在地球历史的早期就已经存在。新的分析还表明，晚期约40亿年前的Hadean磁场很强，这可能表明核心中的化学沉淀在为Geodynamo提供动力。该小组将使用一种古磁方法来进一步测试和填补Paleysensity唱片建筑的空白，这是对Eoarchian最近在其他全球地点的Hadean碎屑锆石的发现。具体而言，他们将从西澳大利亚，印度和南部非洲的新地区产生跨越数十亿年的记录。他们将与一支跨越6个国家的国际合作者一起进行多学科实验室研究（包括光和扫描电子显微镜，聚焦的离子束切片，视图和升降机，传输电子显微镜，磁光kerr效应测量，超敏感的3个组件电流超级结合量式元素（Squid squid squid squid squid），高分辨率离子微探针（虾）分析和次级离子质谱法（SIMS）]。该团队将使用这些新数据来测试每个记录的内部保真度，测试记录之间的一致性，并进一步探索对行星磁屏蔽和核心化学演变的影响。这项工作将支持将在多学科分析中接受广泛培训的毕业生和本科生。这项工作将有助于博士学位。和M.S.这些。调查人员将通过主持讲师和学生的计划继续向罗切斯特中学推广。该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响评估标准，被视为通过评估而被视为珍贵的支持。