Particles to Planets: Unravelling the history of our magnetic field

地球发电机是地球核心的发动机，产生保护磁场。今天，地球发电机的动力来自于铁在不断增长的固体内核上的冻结，但在过去，地球发电机被认为是由纯热能驱动的，就像一锅沸水一样。这两种能源之间的转换代表了地球上最大的能源转换。当它发生时，以及在切换期间保持“引擎运行”的电源并没有得到很好的约束。地球磁场是由地球发电机产生的，所以地球古代磁场的变化可能是探测这种能量转换的唯一方法。地球发电机的能量转换代表着垂死的热电源，应该以一个极弱磁场的时期为标志。这种弱磁场可以保存在岩石中，因为在岩石中发现的纳米级磁性颗粒锁定了它们形成的古代磁场的记忆。然而，随着时间的推移，这些磁记忆会消失，但对于一些粒子来说，它们的记忆消失得比我们预期的要快得多，从而产生了古代地球的错误记录，这些记录似乎比实际情况要弱。我们对地球动力能量转换的最佳估计是在埃迪卡拉纪，大约5.5 -6亿年前。最近对这一时期的研究表明，磁场非常微弱，比今天的磁场弱十倍以上，这可能表明在转变之前，一个垂死的热驱动发电机。然而，其中一些研究的结果具有典型的健忘磁粒子的特征。这就提出了一个关键的问题：“健忘”的岩石发出的微弱信号是否与正在经历重大能量转换的微弱发电机混淆了？为了解决这个问题，我们正在使用一种开创性的新方法，将用于确定古代磁场强度的实验室实验与模拟磁性颗粒行为的最新理论进展无缝集成。采集保存了弱埃迪卡拉磁场的样本，我们将把它们分解成组成它们的磁性粒子。然后，使用新的微磁模型（在分子水平上预测磁性行为的模型），我们将对样品进行数值重组并模拟它们的磁地质历史。通过这种方法，我们将确定这些样品记住的弱场是否忠实地记忆了5亿年前的场，以及这对地球经历了一次重大的内部力量转变的影响。此外，有了这个整合实验观察和新兴理论的新工作流程，将有可能应用我们的开创性技术来解决关键的古岩石和环境问题，这些问题跨越了不同的学科范围，从构造学到考古学，从火山学到月球、火星和其他行星体的演化。

The geodynamo is the engine at the heart of our planet generating our protective magnetic field. Today, the geodynamo is powered by the freezing of iron onto the ever-growing solid inner core, but in the past the geodynamo is thought to have been driven by purely thermal energy, just like a pot of boiling water. The switching between these two power sources represents Earth's largest energy transition. When it happened, and what power source kept "the engine running" during the switch is not well constrained. Earth's magnetic field is generated by the geodynamo, so changes in Earth's ancient magnetic field may be the only way to detect this energy transition.The geodynamo energy transition represents the dying thermal power source and should be marked by a period of extremely weak magnetic field. This weak field can be preserved in rocks because nanoscale magnetic particles found within them lock in memories of the ancient magnetic fields in which they formed. However, over time these magnetic memories fade, but for some particles, their memories fade much faster than we expect, giving rise to false records of the ancient Earth, which appear to be weaker than they really are.Our best estimate for the geodynamo energy transition is during the Ediacaran, around 550-600 million years ago. Recent studies of this time period have revealed an extremely weak magnetic field, more than ten times weaker the field today, which may indicate a dying thermally driven dynamo just prior to the transition. The results from some of these studies, however, have characteristics that are typical of forgetful magnetic particles. This raises a critical question: Are weak signals from "forgetful" rocks being confused with a weak dynamo undergoing a major energy transition?To address this, we are using a pioneering new approach to seamlessly integrate the laboratory experiments used to determine ancient field strengths with recent theoretical advances in simulating the behavior of magnetic particles. Taking samples that preserve a weak Ediacaran field, we will decompose them into their constituent magnetic particles. Then, using new micromagnetic models (models that predict magnetic behavior at the molecular level) we will reassemble the samples numerically and simulate their magneto- geological history.With this approach we will determine if the weak field these samples remember is a faithful memory of the field half a billion years ago and the implications this has for Earth as it experienced a major transition of its internal power. Furthermore, with this new workflow for integrating experimental observations and emergent theory, it will be possible to apply our pioneering techniques to tackle key paleo-, rock and environmental questions spanning a diverse range of disciplines, from tectonics to archeology, or volcanology to the evolution of the Moon, Mars and other planetary bodies.