Silicate and Thermoelectric Dynamos in the early Earth

早期地球的硅酸盐和热电发电机

• 批准号: 2223935
• 负责人: Lars Stixrude
• 金额: $ 56.43万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2223935&HistoricalAwards=false
• 关键词: Silicate; Thermoelectric; Dynamos; early; Earth

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.

磁场是我们星球的一个古老特征，可以追溯到至少35亿年前。这个磁场将屏蔽早期的地球，使早期的生命得以繁衍。然而，这块古老的油田是如何产生的还不得而知。我们认为产生今天和过去10亿年油田的机制：一台发电机，通过冻结液体外核来形成不断增长的固体内核，不可能运行，因为内核早期太热了。但地核可能并不是地球早期唯一的金属区域。早期的地球可能已经足够热，足以维持岩石地幔的深层熔融部分：底部岩浆海洋。最近的结果表明，深部地幔熔融状态的导电性比之前认为的要大得多。这些发现突出表明，需要更多地了解熔岩是如何在高压和高温下变成金属的，并需要调查关于古场起源的两种假说：一种是位于底部岩浆海洋中的硅酸盐发电机，另一种是由横跨核-地幔边界的洋流产生的热电发电机，其机制类似于热电偶的运行。该奖项下的研究将通过使用第一原理量子力学模拟预测关键材料特性来检验这些假设。这项研究将丰富我们对早期地球的认识，并影响到许多研究领域，包括地球内部的动力学和化学演化，以及地表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电子传输的基本物理的理解，并有助于指导未来的实验设计。该项目将支持对一名研究生进行先进材料模拟和地球物理应用方面的培训。这项研究的结果将通过从头预测高压下硅酸盐液体的电子传输性质，使早期磁场产生的两个假设受到基本检验：一个是驻留在底部岩浆海洋中的硅酸盐发电机，另一个是由横跨核-地幔边界的电流产生的热电发电机。该项目将根据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。重点讨论了压力、温度和组成对电导率、电子对热导率的贡献和塞贝克系数的影响。导电性对于了解基底岩浆海洋中硅酸盐发电机的可能存在和行为是很重要的。导热系数对于理解热演化很重要，它设定了硅酸盐发电机运行所必须超过的绝热热流。塞贝克系数是热电发电机运行的关键。这些模拟基于密度泛函理论和Kubo-Greenwood的电子传输理论，将提供对液体中电子传输的基本认识，并将通过光学反射率与实验测量直接联系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Mantle Phase Changes Detected From Stochastic Tomography

从随机断层扫描中检测到地幔相变

• DOI: 10.1029/2022jb025035
• 发表时间: 2023
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Cormier, Vernon F.;Lithgow‐Bertelloni, Carolina;Stixrude, Lars;Zheng, Yingcai
• 通讯作者: Zheng, Yingcai

Melting of MgSiO3 determined by machine learning potentials

• DOI: 10.1103/physrevb.107.064103
• 发表时间: 2023-02-13
• 期刊: PHYSICAL REVIEW B
• 影响因子: 3.7
• 作者: Deng, Jie;Niu, Haiyang;Stixrude, Lars
• 通讯作者: Stixrude, Lars