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.

磁场是地球的一个古老特征，可以追溯到至少35亿年前。 这个磁场会保护早期的地球，使早期的生命得以蓬勃发展。 然而，这个古老的领域是如何产生的还不得而知。 我们认为，在过去的10亿年里，产生磁场的机制是：由液态外核冻结形成不断增长的固态内核的发电机，它不可能运行，因为内核在早期太热了，但内核可能不是早期地球上唯一的金属区域。 早期的地球可能已经热到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，深部地幔的电导率，在熔融的形式，比以前认为的要大得多。 这些发现强调了需要更好地了解熔融岩石如何在高压和高温下变成金属，并调查古代领域起源的两种假设：硅酸盐发电机，在基底岩浆海洋中托管，以及由电流产生的热电发电机穿过核幔边界，在一种类似于热电偶的操作机制。 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测试这些假设。 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电子传输基本物理的理解，并有助于指导未来实验的设计。 该项目将支持对一名研究生进行先进材料模拟和电子物理学应用方面的培训。 这项研究的结果将受到两个假设的产生早期磁场的基本测试，通过预测从头计算的硅酸盐液体在高压下的电子输运性质：硅酸盐发电机，在基底岩浆海洋托管，和热电发电机产生的电流通过核幔边界。 该项目将从第一原理计算决定地球上可能存在硅酸盐和热电发电机的关键物理特性。 重点是压力，温度和组成的电导率，电子的热导率的贡献，和塞贝克系数的值上的作用。 电导率对于了解基底岩浆洋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重要的，并且设置了必须超过硅酸盐发电机才能运行的绝热热通量。 塞贝克系数是发电机热电贡献的关键。 该模拟基于密度泛函理论和Kubo-Greenwood电子输运理论，将提供对液体中电子输运物理的基本见解，并将通过光学反射率与实验测量直接联系。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值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