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，其历史至少可以追溯到 35 亿年前。 这个磁场会屏蔽早期的地球，让早期的生命得以繁盛。 然而，这片古老的油田是如何产生的却不得而知。 我们认为负责产生今天和过去十亿年磁场的机制：通过冻结液体外核以形成不断增长的固体内核提供动力的发电机无法运行，因为核心在早期太热。 但地核可能不是早期地球唯一的金属区域。 早期地球可能足够热，足以维持岩石地幔的深层熔融部分：基底岩浆海洋。 最近的结果表明，熔融形式的深部地幔的电导率比以前认为的要大得多。 这些发现强调需要更深入地了解熔融岩石在高压和高温下如何变成金属，并研究关于古代磁场起源的两种假设：位于基底岩浆海洋中的硅酸盐发电机和热电发电机发电机由穿过核幔边界的电流产生，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。 这项研究将增进我们对极端条件下控制电子传输的基础物理的理解，并有助于指导未来实验的设计。 该项目将支持研究生在先进材料模拟和地球物理学应用方面的培训。 这项研究的结果将通过从头开始预测高压硅酸盐液体的电子传输特性，对早期磁场产生的两个假设进行基本测试：位于基底岩浆海洋中的硅酸盐发电机和热电发电机由穿过核幔边界的电流产生。 该项目将从第一原理计算出控制地球上可能存在的硅酸盐和热电发电机的关键物理特性。 重点是压力、温度和成分对电导率值、电子对热导率的贡献以及塞贝克系数的影响。 电导率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非常重要。 导热率对于理解热演化非常重要，并设定了硅酸盐发电机运行必须超过的绝热热通量。 塞贝克系数是发电机热电贡献运行的关键。 这些模拟基于密度泛函理论和电子传输的 Kubo-Greenwood 理论，将为液体中控制电子传输的物理提供基本见解，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，并被认为值得支持。

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