Evidence for an oxygen-depleted liquid outer core of the Earth
Evidence for an oxygen-depleted liquid outer core of the Earth
复制标题
地球外核存在贫氧液体的证据
DOI：
10.1038/nature10621
复制
发表时间：
2011-11-24
期刊：
影响因子：
64.8
通讯作者：
Gong, Zizheng
中科院分区：
文献类型：
--
作者：
Huang, Haijun;Fei, Yingwei;Gong, Zizheng
根据地球物理观测、宇宙化学约束和高压实验数据，地球的液态外核主要由液态铁和约10%（按重量计）的轻元素合金组成（1，2）。虽然轻元素的浓度很小，但它们仍然影响着地球的核心：它的冷却速度，内核的增长，核心对流的动力学以及地球发电机的演变。几种轻元素--包括硫、氧、硅、碳和氢--已经被提出，但地核中轻元素的确切身份仍然不清楚。氧被认为是核心中的主要轻元素，这是基于宇宙化学的论点和吸积过程中的化学反应（5，6）。它在地核中的存在对地球的氧化状态、压力和温度的吸积条件有直接的影响。在这里，我们报告新的冲击波数据的Fe-S-O系统，直接适用于外核。这些数据包括密度和声速测量，我们观察到的密度和速度分布的液体外核进行比较。结果表明，我们可以排除氧作为一个主要的轻元素在液态外核，因为加入氧到液态铁不会再现同时观察到的密度和声速外核的轮廓。一个贫氧的核心意味着在早期地球吸积过程中的环境更加还原。
On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of light elements(1,2). Although the concentrations of the light elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo(3,4). Several light elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested(2), but the precise identity of the light elements in the Earth's core is still unclear. Oxygen has been proposed as a major light element in the core on the basis of cosmochemical arguments and chemical reactions during accretion(5,6). Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major light element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.