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.

磁场是我们星球的古老特征，其历史可以追溯到至少35亿年前。 这个磁场会掩盖地球早期，使早期生命蓬勃发展。 然而，如何生产古代领域是未知的。 我们认为的机制负责在今天和过去的十亿年中产生该领域：通过冻结液体外芯以形成增长的固体内芯而动力的发电机，因为芯很早就太热了，因此无法操作。 但是核心可能不是地球早期的唯一金属区域。 早期的地球可能已经足够热，可以维持岩石地幔的深层熔融部分：基底岩浆海洋。 最近的结果表明，熔融形式的深地幔的电导率比以前想象的要大得多。 这些发现凸显了需要更深入地了解熔融在高压和温度下如何变成金属，以及对古代田地起源的两个假设的研究：一种硅酸盐发电机，托有在基底岩浆海洋中的硅酸盐发电机，以及由跨核心边界的电流产生的热电发电机，在核心界面上产生的机械机制，具有热效应的机制。 根据该奖项的研究将通过使用第一原理量子力学模拟来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地球早期的理解，并影响许多研究领域，包括内部的动态和化学演化，表面条件以及生命的早期演变。 这项研究将在极端条件下提高我们对电子传输的基本物理学的理解，并有助于指导未来实验的设计。 该项目将支持对高级材料模拟的研究生培训，并应用于地球物理。 这项研究的结果将通过预测高压下硅酸盐液体的电子传输性能来对早期磁场产生的两个假设进行基础测试：一种硅酸盐发电机，托有基础岩浆海洋中的硅酸盐发电机，以及由跨核心边界的电流产生的热电发电机。 该项目将从第一原理中计算出硅酸盐可能存在的关键物理特性和地球热电发电机的存在。 重点是压力，温度和组成对电导率值，对导热率的电子贡献以及Seebeck系数的作用。 电导率对于理解基底岩浆海洋中托管的硅酸盐发电机的可能存在和行为很重要。 热导率对于理解热演化并设置绝热热通量必须超过硅酸盐发电机才能运行至关重要。 Seebeck系数是对发电机热电贡献运行的关键。 基于密度功能理论和电子传输的库拜绿木理论的模拟将提供对液体中电子传输的物理学的基本见解，并将通过光学反射率直接与实验测量接触。该奖项反映了NSF的法定任务，并通过评估了基金会的Merit和Broadial and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and Broadia and tobleit。

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