VIRGIL: The VIRtual paleomaGnetIc Laboratory

地球磁场从形成之初就是我们星球的一部分，但它发生的过程仍然没有被很好地理解。1600年，威廉·吉尔伯特的第一个磁学理论在他的论文《de Magnete，Magneticisque Corporation ibus，et de Magno Magnete Tellure(关于磁体和磁体，以及在那个大磁体上地球)》中提出了最早的地磁学理论之一。通过观察磁石(自然形成的磁铁矿)，吉尔伯特提出地球是一个巨大的偶极磁体，但该理论没有考虑到地球上许多小范围的磁场变化，如南大西洋磁异常。现代地磁学理论认为，磁场是由围绕固体铁核旋转的巨大液态铁海洋形成的--这一点的证据存在于现代观测--磁场的精细结构。但过去的赛场情况又如何呢？幸运的是，含有小规格磁性材料的岩石可以记录并保留地球数千年来的远古磁场，就像磁带可以用来记录信息一样。不幸的是，就像磁带在太阳下放置太久一样，天然岩石受到许多外部因素的影响，这些因素扭曲了它们记录的古老信号。这是古磁学和岩石磁学的任务，目的是设计实验来“清理”信号并恢复古场。但是我们怎么知道我们找回的是真正的古代记录呢？这是通过准确地了解每个小颗粒对加热、变化的外场和其他过程(如化学变化)的反应来实现的。关于地球场的知识不仅讲述了我们星球如何形成的物理过程的故事，也讲述了人类文化的故事。它限制了考古遗址的年代，并让我们了解这些遗址是如何被用于烹饪或锻造金属的。它告诉我们自然灾害，如野火和流离失所的人口。古老的磁场一直伴随着我们或地球，但支持恢复这些重要信息的实验的物理理论是缺陷的。目前的天然材料磁记录理论是由Néel和Stoner&Wohlfarth设计的，现在已经有70年的历史了。它只占岩石中磁性矿物的颗粒大小和几何形状的一小部分；但恢复古地磁信号的实验方案和分析工具仍然建立在这个模型的基础上。在这项提议中，我将通过使用微磁建模、大数据和机器学习方法来彻底改革磁记录理论，以建立从地面到地面的岩石记录过程的完整模拟。这将使我能够重温古地磁记录，并回答这样一个问题：“这是一个好的记录器吗？”这种对现有古地磁记录的评估是至关重要的，因为它限制了地球发电机模型，并使我们能够窥视地球的深层过去。不仅如此，它还将帮助我们建立模型，使我们能够研究地球发电机的未来。

Earth's magnetic field has been part of our planet from early on its formation, but the processes by which it occurs are still not well understood. The first theory of magnetism by William Gilbert proposed one of the first theories of geomagnetism in his treatise "De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on That Great Magnet the Earth)" in 1600. By observing lodestone (naturally occurring magnetite deposits), Gilbert proposed that the Earth was a giant dipolar magnet, but the theory didn't account for the many small-scale variations in Earth's field over the globe such as the south Atlantic magnetic anomaly. Modern theories of geomagnetism propose that the field is formed by a vast ocean of liquid iron swirling around a solid iron core - and evidence of this exists in modern day observations the fine structure of the field. But what about the field in the past? Fortunately, rocks containing small specs of magnetic materials can record and retain Earth's ancient field over millennia, in the same way that magnetic tape can be used to record information. Unfortunately, like magnetic tape left in the sun too long, natural rocks are subject to many external factors that distort the ancient signal that they record. It is the task of palaeo- and rock magnetism to devise experiments to "clean" the signal and recover the ancient field. But how do we know that the field that we recover is the true ancient recording? This is done by understanding precisely how each small grain behaves in response to heating, changing external field and other processes (such as chemical alteration).Knowledge of Earth's field tells not just the story of the physical processes of how our planet was formed - it is also the story of human culture. It constrains dates of archaeological sites and gives us an understanding of how those sites were used, be it for cooking or the forging of metals. It tells us of natural disasters such as wildfires and the displacement human populations. The ancient field has always been with us and or planet, but the physical theories that underpin experiments to recover this vital information is flawed.The current theory of magnetic recording in natural materials was devised by Néel and Stoner & Wohlfarth and is now 70 years old. It accounts for only a tiny fraction of the grain sizes and geometries of magnetic minerals found in rocks; but the experimental protocols and analytical tools to recover the palaeomagnetic signal are still being built on this model. In this proposal I will overhaul magnetic recording theory by using micromagnetic modelling, big-data and machine learning methods to build a complete simulation of the recording process in rocks from the ground up. This will enable me to revisit the palaeomagnetic record and answer the question: "is this a good recorder"? Such an evaluation of the existing palaeomagnetic record is critical since it constrains geodynamo models and allows us to peer into the deep past of our planet. Not only that, but it will also help underpin the models that will allow us to investigate the future of the geodynamo.