Collaborative Research: Geomagnetic field strength and stability between 500 and 800 Ma: Constraining inner core growth

合作研究：500 至 800 Ma 之间的地磁场强度和稳定性：限制内核生长

• 批准号: 1828825
• 负责人: Kenneth Kodama
• 金额: $ 30.7万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-04-15 至 2024-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1828825&HistoricalAwards=false
• 关键词: Collaborative; Research; Geomagnetic; field; strength

Earth's magnetic field protects the planet from solar particles that would otherwise erode the atmosphere. Thus, the magnetic field is thought to be an essential factor ensuring long-term planetary habitability. Today, this geomagnetic field is powered by growth of the solid inner core. But thermal models suggest Earth has not always had a solid inner core; the time of the onset of inner core growth has ranged from 500 million to more than 2.5 billion years ago. This represents a fundamental unknown about the planet. Arguably the best way to investigate this question is to use "paleomagnetism", the record of the ancient magnetic field trapped in rocks and crystals as they form. Such data have motivated the hypothesis that the geomagnetic field, and the magnetic shielding of the atmosphere from solar particles, almost collapsed 565 million years ago, but then the field slowly recovered. This event may record the birth of the solid inner core. This hypothesis will be tested through studies of rocks ranging in age from 800 to 500 million years old found in Australia, Canada and the United States. The collaborative work will involve a team of 5 scientists at 3 institutions (including an underrepresented minority and woman scientist), and will be integrated into education and outreach efforts at each university, including efforts to expand opportunities for first-generation and historically underrepresented individuals. The time of Earth's inner core nucleation (ICN) is unknown and thus represents a first-order problem in our understanding of the planet. For decades the inner core was assumed to be billions of years old. However, viable core thermal conductivity values now span a factor of 3, with the highest values compatible with ICN onset between approximately 800 and 500 million years ago. These onset ages are predicted by many recent thermal evolution models, but a paucity of paleofield strength data has thwarted efforts seeking to determine if there is a sign of a young inner core. Recent paleomagnetic data record an unprecedented low in time-averaged geomagnetic field strength 565 million years ago that is greater than 10 times lower than the strength of the present geomagnetic field. The ultra-low field intensity is accompanied by an ultra-high reversal frequency and other indicators of unusual field behavior in 15 other Latest Precambrian-Cambrian igneous and sedimentary units. These observations and recent modeling results are the basis for the hypothesis that the geomagnetic field approached collapse in late Precambrian/early Cambrian times (i.e., the ratio of the magnetic energy to kinetic energy is less than 1) coincident with the onset of ICN. Hence, the inner core may be young. This hypothesis will be tested through the study of 4 igneous provinces emplaced between about 500 and 800 million years ago, in Australia, the US and the Northwest Territories (Canada). State-of-the-art paleomagnetic directional and paleointensity data, including single silicate crystal analyses, and U-Pb radiometric age data will allow a synoptic view of the geodynamo during the youngest predicted ages of ICN. The work will involve a team (5 PIs/co-PIs at 3 institutions) including an underrepresented minority and woman scientist. The work will be integrated into undergraduate and graduate education and outreach efforts at each university, including efforts to expand opportunities for first-generation and historically underrepresented individuals. Student teams will visit and conduct analyses in each of the laboratories, comparing and contrasting techniques. The project will be integrated into university-specific undergraduate courses in preparation for field and laboratory investigations.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.

地球的磁场可保护行星免受太阳颗粒的影响，否则会侵蚀大气。因此，磁场被认为是确保长期行星宜居性的重要因素。如今，这个地磁领域由固体内核的增长提供动力。但是热模型表明，地球并不总是具有坚实的内核。内部核心增长的发作时间从5亿到25亿年前不等。这代表了关于地球的基本未知。可以说，调查这个问题的最佳方法是使用“古磁性”，这是古老的磁场的记录，它们在形成时被困在岩石和晶体中。这样的数据激发了以下假设：地磁场以及大气中太阳颗粒的磁屏蔽几乎在5.65亿年前倒塌，但随后该领域慢慢恢复了。该事件可能会记录固体内核的诞生。该假设将通过研究在澳大利亚，加拿大和美国的800至5亿年龄段的岩石的研究来检验。合作工作将涉及3个机构的5位科学家组成的团队（包括代表性不足的少数群体和女科学家），并将纳入每所大学的教育和宣传工作，包括为扩大第一代和历史上代表性不足的人的努力。地球内核成核（ICN）的时间是未知的，因此在我们对行星的理解中代表了一阶问题。几十年来，内部核心被认为是数十亿年的历史。但是，现在可行的核心热导率值占3倍，最高值与ICN发作兼容大约800到5亿年前。这些开始年龄是通过许多最近的热进化模型预测的，但是对古野强度数据的匮乏阻碍了人们寻求确定是否存在年轻内核的迹象。最近的古磁数据记录了5.65亿年前时间平均的地磁场强度前所未有的低点，比目前的地磁场的强度低10倍。超低场强度伴随着超高的逆转频率和其他15个最新最新的前寒武纪 - 夏布和沉积单元中异常野外行为的指标。这些观察结果和最新的建模结果是假设的基础：在前寒武纪晚期/早期寒武纪时代（即磁能与动能的比率小于1）中，地磁磁场接近倒塌的基础。因此，内部核心可能年轻。该假设将通过对大约500到8亿年前的4个火成岩省进行的研究进行检验，澳大利亚，美国和西北地区（加拿大）。最先进的古磁定向和古显着数据，包括单硅酸盐晶体分析以及U-PB辐射年龄数据，将允许在最年轻的ICN预测年龄期间对Geodynamo的概要视图。这项工作将涉及一个团队（3个机构的5个PI/Co-Pis），其中包括代表性不足的少数群体和女性科学家。这项工作将纳入每所大学的本科和研究生教育以及外展工作，包括为扩大第一代和历史上代表性不足的人的机会而努力。学生团队将在每个实验室中访问并进行分析，以比较和对比技术。该项目将被整合到大学特定的本科课程中，以准备进行现场和实验室调查。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审查标准，认为值得通过评估来获得支持。