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，产生于液态铁核，保护大气层免受来自太阳的粒子流，称为“太阳风”。如果没有这个防护罩，大气层就会被侵蚀，水就会流失，特别是在地球年轻和太阳风强烈的时候。因此，了解地球最早的磁场可以为我们星球的核心和大气层的演变提供独特的见解。因为水是我们所知的生命所必需的，这一知识也关系到地球可居住性的起源。唯一已知的能够准确记录这种早期磁性历史的物质是锆石，现在在较年轻的沉积岩中发现了微小的颗粒。其中一些锆石是引人注目的，因为它们含有更小的内含物，可以保存数十亿年前的古代磁场信号。但由于这些锆石非常小--只有人类头发丝的几倍厚--测量它们的磁性极具挑战性。研究人员开发并应用了新技术来表征锆石中磁性包裹体的性质，并使用大量高灵敏度仪器来检索它们的磁信号。他们的测量结果表明，至少在42亿年前存在磁场。这些数据表明大气屏蔽已经就位。它们还限制了导致产生强磁场的核心物理条件。研究人员将填补磁场历史的空白，从西澳大利亚州，印度和南部非洲的新锆石地点获得数据。他们将与跨越6个国家的国际合作者团队合作进行多学科实验室研究。然后，研究小组将使用这些新数据来测试磁历史的保真度，并进一步探索磁屏蔽和地球演化的影响。这项工作将支持研究生和本科生，他们将在该领域和多学科分析方面接受广泛的培训，并将包括通过为教师和学生举办的项目与罗切斯特中学进行外联。地磁场最早历史的知识可以为我们理解地核、大气和地球可居住性的演变提供关键的见解。唯一已知的材料，可以准确地定年，并能够记录这段历史的数亿年的时间尺度，需要推进我们的理解这些基本问题的地球演化是始新世到冥古宙锆石轴承微小的磁性夹杂物，现在发现在年轻的沉积单元。然而，锆石的磁性测量，以及对其磁化强度的询问以确定它们是否保留原始信号，是需要多学科方法的艰巨技术挑战。研究人员最近提出了新的古地磁、电子显微镜、地球化学和古强度数据，表明西澳大利亚州杰克山精选锆石中存在原生磁铁矿包裹体。这些新的数据进一步支持了杰克山锆石记录地球发电机的主要磁性信号，其记录可以追溯到约42亿年前。因此，这些分析表明，磁层对大气层的屏蔽在地球历史的早期就已经存在。新的分析还表明，在大约40亿年前的冥古宙晚期有一个强大的磁场，这可能是一个信号，表明地核中的化学沉淀为地球发电机提供了动力。该团队将使用古地磁方法，进一步测试和填补在最近发现的始新世到冥古宙碎屑锆石在其他全球网站的古强度记录建设的差距。具体来说，他们将从西澳大利亚、印度和南部非洲的新地点产生跨越数百万年的记录。他们将与一个来自6个国家的国际合作者团队合作，进行多学科实验室研究[包括光学和扫描电子显微镜、聚焦离子束切片和观察、透射电子显微镜、磁光克尔效应测量、超灵敏三分量直流超导量子干涉器件（SQUID）磁力测量、扫描SQUID显微镜磁力测量、灵敏的高分辨率离子微探针（SHRIMP）分析和二次离子质谱（西姆斯）]。该团队将利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，并进一步探索行星磁屏蔽和核心化学演化的影响。这项工作将支持研究生和本科生，他们将接受多学科分析的广泛培训。这项工作将有助于博士学位。和史密斯论文调查人员将继续推广到罗切斯特中学举办项目的教师和学生。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。