Geophysics of Iron in the Earth’s Core

地核位于地壳以下近3000公里处，是地球上最偏远的地区。地核的外壳主要由铁组成，是液态的，而其最内部的部分，即内核，是固态的。地核在地球的地磁、动力过程和热演化中起着核心作用。在这里，研究小组在地球深处普遍存在的极端压力和温度下进行实验室实验。他们测量了构成地核的富含铁的材料的特性，例如，它们的变形机制和粘度。这些属性在核心条件下会发生显著变化。研究结果揭示了地震波在内核不同部位以不同速度传播的原因。它们限制了地球磁场是如何产生的，并揭示了它过去的演变。这些结果对许多研究地球深部过程的研究人员很有价值：矿物物理学家、地震学家和地球动力学家。该项目促进了跨学科、地球科学和材料科学以及工业领域有用的技术进步。它还为一名女研究生提供支持，为本科生提供培训，并向K-12学生和公众提供服务。该项目旨在表征铁和富铁化合物和合金在地球深处极端条件下的关键流变特性。解决了两个基本问题：(1)是什么导致了内核地震各向异性？(2)外核的粘性耗散如何影响地球动力的演化？为了解决第一个问题，研究小组描述了固体铁在高压和高温下的主要变形机制和强度。还测量了铁结晶过程中形成的晶格择优取向。目的是了解在凝固或随后的变形（或两者兼有）过程中如何获得弹性各向异性铁晶体的排列。为此，研究人员在电阻和激光加热的金刚石砧细胞中进行了静态压缩实验。他们在国家同步加速器设施中进行原位x射线成像和衍射测量。解决第二个问题需要测量核心条件下的铁粘度。虽然传统的测量仅限于较低的压力，但团队受益于新技术的发展；这为测量动态压缩到外岩心条件下的铁的粘度提供了途径。因此，该团队在直线加速器相干光源（SLAC）的极端条件下的材料仪器和劳伦斯利弗莫尔国家实验室的国家点火设备上进行了动态压缩实验，并使用了新的x射线衍射和成像技术。这些实验提供了新的机会，可以利用国家实验室现有的大量资源和专业知识，并将其应用于更好地了解地球。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。

Located nearly 3000 km below the crust, the Earth’s core is the most remote region within our planet. Mainly composed of iron, the core’s outer shell is liquid while its most inner part, the inner core, is solid. The core plays a central role in the planet’s geomagnetism, dynamic processes, and thermal evolution. Here, the team conducts laboratory experiments at the extreme pressures and temperatures prevailing in Earth’s deep interior. They measure the properties of the iron-rich materials that make up the core, e.g., their deformation mechanisms and viscosity. These properties can be dramatically altered at core conditions. The results give insight into why seismic waves travel at different speeds through different parts of the inner core. They constrain how the Earth’s magnetic field is generated and unveil its past evolution. These outcomes are valuable to many researchers studying deep Earth’s processes: mineral physicists, seismologists, and geodynamicists. The project promotes technical advances useful across disciplines, in geoscience and materials science, and in the industry. It also provides support for a female graduate student, training for undergraduate students, and outreach toward K-12 students and the public.The project aims at characterizing key rheological properties of iron and iron-rich compounds and alloys at the extreme conditions of the deep Earth. Two fundamental questions are addressed: (1) What causes inner-core seismic anisotropy? (2) How does viscous dissipation in the outer core influence the evolution of the geodynamo? To address the first question, the team characterizes the dominant deformation mechanisms and strength of solid iron at high pressures and temperatures. The lattice preferred orientation that develops during iron crystallization is also measured. The goal is to understand how the alignment of elastically anisotropic iron crystals may be acquired during solidification or subsequent deformation (or both). To this aim, the researchers carry out static compression experiments in resistive and laser-heated diamond anvil cells. They perform in situ X-ray imaging and diffraction measurements at national synchrotron facilities. Addressing the second question requires measuring iron viscosity at core conditions. While traditional measurements are limited to lower pressures, the team benefit from new technical developments; these enable a path toward measuring the viscosity of iron dynamically compressed to outer core conditions. Thus the team carries out dynamic compression experiments and use novel X-ray diffraction and imaging techniques at the Materials at Extreme Conditions instrument at the Linac Coherent Light Source (SLAC) and the National Ignition Facility at Lawrence Livermore National Laboratory. These experiments represent new opportunities to leverage the considerable resources and expertise available at national laboratories and apply them to better understand the Earth.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.