Particles to Planets: Unravelling the history of our magnetic field

地球发电机是我们星球中心的引擎，产生我们的保护性磁场。今天，地球发电机是通过将铁冻结在不断增长的坚固内核上来提供动力的，但在过去，地球发电机被认为是由纯粹的热能驱动的，就像一锅沸水一样。这两种能源之间的切换代表着地球上最大的能源转换。当它发生的时候，在切换过程中是什么动力来源保持“发动机运转”并没有得到很好的约束。地球的磁场是由地球发电机产生的，因此，地球古代磁场的变化可能是探测这种能量转换的唯一途径。地球发电机的能量转换代表着濒临死亡的热能来源，应该以极弱的磁场为标志。这种微弱的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形成它们的古老磁场的记忆。然而，随着时间的推移，这些磁性记忆会褪色，但对一些粒子来说，它们的记忆褪色的速度比我们预期的要快得多，这导致了关于古代地球的虚假记录，这些记录似乎比实际情况更弱。我们对地球发电机能量转换的最佳估计是在大约5.5亿-6亿年前的埃迪卡拉纪。最近对这段时间的研究揭示了一个极弱的磁场，比今天的磁场弱十多倍，这可能表明就在过渡之前，一台濒临死亡的热驱动发电机。然而，其中一些研究的结果具有典型的健忘磁性粒子的特征。这就提出了一个关键问题：来自“健忘”岩石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最近在模拟磁性粒子行为方面的理论进展无缝地结合在一起。取一些保存有微弱埃迪卡拉磁场的样本，我们会将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行为的模型)，我们将以数字方式重新组装样品，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是5亿年前磁场的忠实记忆，以及这对经历了内部力量重大转变的地球的影响。此外，有了这一整合实验观测和新兴理论的新工作流程，我们将有可能应用我们的开创性技术来解决跨越各种学科的关键古、岩石和环境问题，从构造学到考古学，或从火山学到月球、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.