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。主要由铁组成，核心的外壳是液体，而其最内部的部分，内核，是固体。 地核在地球的地磁、动力学过程和热演化中起着核心作用。在这里，该团队在地球内部深处的极端压力和温度下进行实验室实验。 它们测量构成核心的富铁材料的性质，例如，它们的变形机制和粘度。 这些特性在堆芯条件下会发生显著变化。研究结果揭示了为什么地震波以不同的速度穿过内核的不同部分。它们限制了地球磁场的产生方式，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的技术进步。该项目还为一名女研究生提供支持，为本科生提供培训，并向K-12学生和公众进行宣传。该项目旨在表征铁和富铁化合物和合金在地球深部极端条件下的关键流变特性。两个基本问题得到解决：（1）是什么原因导致内核地震各向异性？(2)外核的粘性耗散如何影响地球发电机的演化？为了解决第一个问题，该团队描述了高压和高温下固体铁的主要变形机制和强度。还测量了在铁结晶过程中发展的晶格优选取向。我们的目标是了解如何在凝固或随后的变形（或两者）过程中获得的弹性各向异性铁晶体的对齐。 为了实现这一目标，研究人员在电阻和激光加热的金刚石砧座中进行了静态压缩实验。他们在国家同步加速器设施进行现场X射线成像和衍射测量。 解决第二个问题需要在核心条件下测量铁的粘度。虽然传统的测量仅限于较低的压力，但该团队受益于新的技术发展;这些技术发展为测量动态压缩到外核条件下的铁的粘度开辟了道路。因此，该团队进行了动态压缩实验，并在Linac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施中使用了新的X射线衍射和成像技术。这些实验代表了利用国家实验室的大量资源和专业知识的新机会，并将其应用于更好地了解地球。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.