Can homogeneous nucleation resolve the inner core nucleation paradox?
Can homogeneous nucleation resolve the inner core nucleation paradox?
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DOI：
10.1016/j.epsl.2023.118176
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发表时间：
2023-07
影响因子：
5.3
通讯作者：
Alfred J. Wilson;D. Alfé;A. Walker;C. Davies
中科院分区：
文献类型：
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作者：
Alfred J. Wilson;D. Alfé;A. Walker;C. Davies
地球固体内核的形成被认为标志着地球深部演化的深刻变化，以及可用于产生地磁场的能量。以前的研究一般认为内核在大约5 - 10亿年前成核，但忽略了这样一个事实，即均匀的液体必须冷却到远低于其熔点才能自发形成固体。经典的成核理论预测，核心必须过冷几百K，这与核心目前温度的估计不一致。这个“内核成核悖论”因此断言，目前的内核不应该形成，在我们对地球深部演化的理解中留下了一个重大的空白。在本文中，我们探讨尚未测试的富铁系统，其中可能包括地球的早期核心的成核过程。我们发现，1摩尔%，与纯铁相比，Si和S分别增加了400 K和1000 K所需的过冷度以冻结内核。10摩尔% O使所需的内核形核过冷度降低到730 K和3 mol.% C到只有612 K，这接近解决悖论，但仍然需要最近形成的内核。
The formation of Earth's solid inner core is thought to mark a profound change in the evolution of the deep Earth and the power that is available to generate the geomagnetic field. Previous studies generally find that the inner core nucleated around 0.5–1 billion years ago, but neglect the fact that homogeneous liquids must be cooled far below their melting point in order for solids to form spontaneously. The classical theory of nucleation predicts that the core must be undercooled by several hundred K, which is incompatible with estimates of the core's present-day temperature. This “inner core nucleation paradox” therefore asserts that the present inner core should not have formed, leaving a significant gap in our understanding of deep Earth evolution. In this paper we explore the nucleation process in as yet untested iron-rich systems which may comprise the Earth's early core. We find that 1 mol.% Si and S increase the supercooling required to freeze the inner core compared to pure iron by 400 K and 1000 K respectively. 10 mol.% O reduces the required inner core nucleation supercooling to 730 K and 3 mol.% C to only 612 K, which is close to resolving the paradox but still requires that the inner core formed recently.