Palaeomagnetic field behaviour in the Palaeozoic and the hunt for inner core birth

古生代的古磁场行为与寻找内核诞生

• 批准号: NE/X014142/1
• 负责人: Andrew Biggin
• 金额: $ 103.82万
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX014142%2F1
• 关键词: Palaeomagnetic; field; behaviour; Palaeozoic; hunt

Through describing and explaining how Earth's magnetic field changed between 330 and 600 million years ago, this project aims to tackle one of the most profound outstanding gaps in our knowledge of the Earth's deep interior: the age of the solid inner core.Earth's magnetic field extends far out into space and shields life on the surface and much of Earth's atmosphere from harmful solar wind. It is generated in the liquid outer core of the planet but the growth of the underlying inner core provides much of the energy to drive it today. Our planet has had a magnetic field for most of its 4.5 billion year history but the solid inner core did not exist for all of this time. Theory predicts that the onset of freezing of solid iron at Earth's centre will have been associated with a sharp increase in the long-term average magnetic field strength from a weak preceding state. We are hunting for this signature of the birth of Earth's inner core which has since grown to be nearly the size of the Moon. If we could definitively identify this moment in Earth's history, then its timing would provide a major constraint on the thermal evolution of the entire planet.Our recent works highlight the next steps required to describe and explain magnetic field behaviour such that we can detect inner core birth. Our measurements have established that, during the time periods 600-540 million years ago and 330-420 million years ago, the magnetic field was anomalously weak compared to more recent times. We now need to know how it evolved between those time periods. If it remained weak through this interval (420-540 million years ago) then this would suggest a much later inner core formation date, and far less magnetic shielding from the sun, than previously thought. As well as determining its average strength during the period for which we currently have no data, we also need to build a more complete picture of how the shape and stability of the global magnetic field changed over the complete period 330 to 600 million years ago. The current configuration of Earth's magnetic field (resembling a bar magnet nearly aligned with the planetary rotation axis) is an effective one for deflecting solar radiation around near-Earth space and avoiding the atmosphere and biosphere. We need to know if this was always the case so that we can constrain models of magnetic shielding and simulations of Earth's core dynamo. Once we have a good description of the long-term magnetic field behaviour, we then need to know how we can reproduce it using simulations of the flow of liquid iron in Earth's core. There are many possible rates of inner core growth and patterns of forcing from the overriding mantle; we need to see which combination of these produces magnetic field behaviour that best matches the observations.We will undertake this research using a multidisciplinary approach building on previous work undertaken by the team. The evolution of field strength will be determined by rigorous palaeomagnetic measurements performed on carefully selected rock samples using our state-of-the-art facilities augmented by a versatile new instrument. The global statistical characterisation of the field will be produced using a novel set of criteria informed by an exhaustive compilation of new and extant datasets. Finally, we will draw on our own suite of core-mantle evolution models, and those of our collaborators, to iterate towards numerical simulations of the Earth's core dynamo that, subject to external influence, optimally reproduce the observations delivered in the other parts of the project. Through using out combination of laboratory experiments, data analyses and numerical simulations, we aim to understand how the magnetic field changed during this period yielding vital information about the evolution of deep Earth's structure and also about the level of protection that early multicellular life had from harmful solar wind radiation.

通过描述和解释 330 至 6 亿年前地球磁场的变化，该项目旨在解决我们对地球深层内部知识中最深刻的空白之一：固体内核的年龄。地球磁场延伸深入太空，保护地表生命和地球大部分大气层免受有害太阳风的影响。它是在地球的液体外核中产生的，但下面的内核的生长提供了今天驱动它的大量能量。我们的星球在 45 亿年历史的大部分时间里都存在磁场，但固体内核自始至终都不存在。理论预测，地球中心固体铁开始冻结将与长期平均磁场强度从先前的弱状态急剧增加有关。我们正在寻找地球内核诞生的标志，地球内核已经发展到接近月球的大小。如果我们能够明确地确定地球历史上的这一时刻，那么它的时间将为整个地球的热演化提供主要约束。我们最近的工作强调了描述和解释磁场行为所需的后续步骤，以便我们能够检测内核出生。我们的测量表明，在 600-5.4 亿年前和 330-4.2 亿年前，磁场与最近时期相比异常弱。我们现在需要知道它在这些时期之间是如何演变的。如果在这段时期（420-5.4亿年前）它仍然很弱，那么这将表明内核的形成日期要晚得多，并且对太阳的磁屏蔽比以前认为的要少得多。除了确定我们目前没有数据的时期的平均强度外，我们还需要更全面地了解 330 至 6 亿年前整个时期全球磁场的形状和稳定性如何变化。当前地球磁场的配置（类似于几乎与行星旋转轴对齐的条形磁铁）是一种有效的配置，可以使太阳辐射偏转近地空间周围并避开大气层和生物圈。我们需要知道情况是否总是如此，以便我们可以约束磁屏蔽模型和地球核心发电机的模拟。一旦我们对长期磁场行为有了很好的描述，我们就需要知道如何通过模拟地核中液态铁的流动来重现它。内核生长速率和来自压倒性地幔的强迫模式有多种可能。我们需要看看其中的哪种组合会产生与观测结果最匹配的磁场行为。我们将在团队之前开展的工作的基础上，采用多学科方法进行这项研究。场强的演变将通过使用我们最先进的设施（通过多功能新仪器增强）对精心挑选的岩石样本进行严格的古地磁测量来确定。该领域的全球统计特征将使用一套新颖的标准来产生，这些标准是对新的和现有的数据集进行详尽的汇编。最后，我们将利用我们自己的一套核心-地幔演化模型以及我们的合作者的模型，迭代对地球核心发电机的数值模拟，在外部影响下，最佳地再现地球其他部分的观测结果。项目。通过实验室实验、数据分析和数值模拟的结合，我们的目标是了解这一时期磁场如何变化，从而提供有关地球深层结构演化的重要信息，以及早期多细胞生命免受有害影响的保护水平。太阳风辐射。