MicroPI: A micromagnetic approach to absolute palaeointensity determinations

发生在地球深处的物理和化学过程塑造了我们星球数十亿年来的演变。我们几乎没有什么工具可以用来研究整个地球地质历史中的深层。其中一个工具是分析岩石产生的地磁场的磁性记录。地磁场是在地表以下3000多公里的地核内产生的，其行为受到自45亿年前地球形成以来一直在缓慢变化的不同化学和热源的改变。地磁场的变化是由岩石在形成时记录下来的。通过采样和分析岩石的磁性记录，我们可以回放这段随时间变化的地磁场记录，并利用这些信息来测试我们星球演化的各种理论。此外，对古代地磁场的了解也使我们能够确定早期地球表面的宜居性，因为众所周知，地磁场可以保护和保持大气不受太阳辐射的剥离。与高度均匀的人造磁记录介质不同，岩石包含各种不同形状和大小的磁性颗粒。众所周知，这些磁性颗粒表现出复杂的磁性行为；然而，到目前为止，一个非常简化的模型一直被用来解释和确定岩石记录的古代地磁场强度。这意味着我们目前用来从岩石中提取古代地磁场信息的理论是不正确的，导致了对古磁场强度的估计错误。这让人怀疑我们目前对过去地磁场强度如何变化的看法，也可能解释了从相同年龄的岩石获得不同结果的多项研究中的不一致。去年，该项目的提出者开发了一个新的理论模型，准确地捕捉到岩石中记录的磁化的复杂行为。在这个项目中，我们建议使用我们对磁性矿物如何记录地磁场的新理解来建立一种全新的、不同的方法来确定岩石中记录的古代地磁场强度。这一新方法将依赖于从数值模型中模拟的不同类型磁性颗粒的磁性特征的大型数值数据库。我们将通过一个网络应用程序向科学界提供这种新方法，地球科学家可以在那里上传他们自己的实验测量结果，并可以使用我们的新方法计算古磁场强度的估计值。通过我们的新方法，我们将研究我们这个时代关于过去45亿年来地球内部热量和热流最紧迫的问题之一：固体内核是什么时候成核的？一些已公布的古地磁数据表明，它最早出现在5亿年前，尽管这一说法存在广泛争议。我们将使用我们的新方法来确定这些磁性数据的可靠性，并更好地定位内核成核的时间。

The physical and chemical processes that occur deep within the Earth have shaped the evolution of our planet over billions of years. We have very few tools that can be used to investigate the deep Earth over its entire geological history. One such tool is the analysis of magnetic recordings of the geomagnetic field made by rocks.The geomagnetic field is generated within the Earth's core more than 3000 km below the surface, and its behaviour is modified by the varying chemistry and sources of heat that have been slowly changing since the Earth's formation 4.5 billion years ago. The changes in the geomagnetic field are recorded by rocks when they form. By sampling and analysing the magnetic recordings of rocks, we can play back this recording of the changing geomagnetic field over time, and use this information to test the various theories of the evolution of our planet. In addition, knowledge of the ancient geomagnetic field also allows us to determine habitability on the early Earth's surface, as the geomagnetic field is known to protect and preserve the atmosphere from Solar radiation stripping.Unlike highly uniform man-made magnetic recording media, rocks contain a wide variety of magnetic particles of different shapes and sizes. These magnetic particles are known to display complex magnetic behaviours; however, until now a very simplified model has been used to explain and determine the ancient geomagnetic field intensities recorded by rocks. This means that the theory we presently use to extract ancient geomagnetic field information from rocks is incorrect, leading to errors in estimates of the ancient field intensity. This casts doubt on our current view of the how the geomagnetic field intensity has varied in the past, and also likely explains inconsistencies in multiple studies where different results are obtained from rocks of the same age.In the last year, the proposers of this project have developed a new theoretical model which accurately captures the complex behaviour of the magnetisations recorded within rocks. In this project, we propose to use our new understanding of how magnetic minerals record the geomagnetic field to build a completely new and different approach for determining ancient geomagnetic field intensities recorded in rocks. This new method will rely on a large numerical database of magnetic characteristics of different types of magnetic particles that have been simulated from numerical models. We will make this new method available to the scientific community through a web-app, where Earth Scientists can upload their own experimental measurements and can calculate estimates of palaeomagnetic field intensities using our new method.With our new approach we will investigate one of the most pressing issues of our times concerning heat and heat flow within the Earth over the last 4.5 billion years: when did the solid Inner Core nucleate? There are some published palaeomagnetic data to suggest that it is as recent as ~500 million years ago, though this is widely disputed. We will use our new approach to determine the reliability of these magnetic data, and to better pinpoint the timing of Inner Core Nucleation.