Silicate and Thermoelectric Dynamos in the early Earth

磁场是地球的一个古老特征，至少可以追溯到35亿年前。这个磁场可能保护了早期的地球，使早期的生命得以繁荣。然而，这个古老的油田是如何产生的还不得而知。我们认为，今天和过去10亿年里产生磁场的机制是：一台发电机通过冻结液态的外核来形成不断增长的固体内核，这台发电机不可能运转，因为内核在早期太热了。但地核可能不是地球早期唯一的金属区域。早期的地球可能足够热，足以维持岩石地幔的深层熔融部分：基底岩浆海洋。最近的研究结果表明，在熔融状态下，深层地幔的导电性比以前认为的要大得多。这些发现强调了对熔融岩石如何在高压和高温下变成金属的需要，以及对古代磁场起源的两种假设的研究：一种是基底岩浆海洋中的硅酸盐发电机，另一种是由穿过核心-地幔边界的电流产生的热电发电机，其机制类似于热电偶的操作。该奖项下的研究将通过使用第一性原理量子力学模拟预测关键材料特性来验证这些假设。这项研究将丰富我们对早期地球的理解，并影响许多研究领域，包括内部的动力学和化学演化，以及表面条件和生命的早期演化。这项研究将促进我们对极端条件下控制电子传输的基本物理的理解，并有助于指导未来实验的设计。该项目将支持培养一名高级材料模拟和地球物理学应用方面的研究生。这项研究的结果将通过从头开始预测硅酸盐液体在高压下的电子传输特性，对早期磁场产生的两个假设进行基本测试：一个是基底岩浆海洋中的硅酸盐发电机，另一个是由穿过核心-地幔边界的电流产生的热电发电机。该项目将从第一性原理计算控制地球上可能存在的硅酸盐和热电发电机的关键物理性质。重点是压力、温度和成分对电导率值、电子对导热系数的贡献和塞贝克系数的作用。电导率对于了解基底岩浆海中可能存在的硅酸盐发电机及其行为具有重要意义。热导率对于理解热演化是很重要的，它设定了硅酸盐发电机必须超过的绝热通量才能运行。塞贝克系数是热电发电机运行的关键。基于密度泛函理论和Kubo-Greenwood电子输运理论的模拟，将为控制液体中电子输运的物理学提供基本的见解，并将通过光学反射率与实验测量直接联系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The magnetic field is an ancient feature of our planet, dating back to at least 3.5 billion year ago. This magnetic field would have shielded the early Earth, allowing early life to flourish. Yet how the ancient field was produced is unknown. The mechanism that we think is responsible for producing the field today and for the last one billion years: a dynamo powered by freezing the liquid outer core to form the growing solid inner core, could not have operated because the core was too hot early on. But the core may not be the only metallic region in the early Earth. The early Earth may have been hot enough to maintain a deep molten portion of the rocky mantle: a basal magma ocean. Recent results show that the electrical conductivity of the deep mantle, in molten form, is much greater than previously thought. These findings highlight the need for a much greater understanding of how molten rock becomes metallic at high pressure and temperature, and the investigation of two hypotheses for the origin of the ancient field: a silicate dynamo, hosted in the basal magma ocean, and a thermoelectric dynamo produced by currents across the core-mantle boundary, in a mechanism akin to the operation of a thermocouple. Research under this award will test these hypotheses by predicting key material properties using first-principles quantum-mechanical simulations. This research will enrich our understanding of the early Earth and impact many fields of study, including the dynamical and chemical evolution of the interior, as well as surface conditions and the early evolution of life. The research will advance our understanding of the fundamental physics governing electron transport at extreme conditions, and help to guide the design of future experiments. The project will support the training of a graduate student in advanced materials simulation and applications to geophysics. The results of this research will subject two hypotheses for the generation of the early magnetic field to fundamental tests by predicting ab initio the electron transport properties of silicate liquids at high pressure: a silicate dynamo, hosted in the basal magma ocean, and a thermoelectric dynamo produced by currents across the core-mantle boundary. The project will compute from first principles the key physical properties governing the possible existence of silicate and thermoelectric dynamos in the Earth. The focus is on the role of pressure, temperature, and composition on the values of the electrical conductivity, the electronic contribution to the thermal conductivity, and the Seebeck coefficient. The electrical conductivity is important for understanding the possible existence and behavior of a silicate dynamo hosted in the basal magma ocean. The thermal conductivity is important for understanding thermal evolution and sets the adiabatic heat flux that must be exceeded for the silicate dynamo to operate. The Seebeck coefficient is key to the operation of a thermoelectric contribution to the dynamo. The simulations, based on density functional theory and the Kubo-Greenwood theory of electron transport, will provide fundamental insight into the physics governing electron transport in liquids, and will make direct contact with experimental measurements via the optical reflectivity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.