Silicon in the Earth's core
Silicon in the Earth's core
复制标题
DOI：
10.1038/nature05927
复制
发表时间：
2007-06-28
期刊：
影响因子：
64.8
通讯作者：
Reynolds, Ben C.
中科院分区：
文献类型：
--
作者：
Georg, R. Bastian;Halliday, Alex N.;Reynolds, Ben C.
行星中硅酸盐矿物之间的微小同位素差异可能是由于与核心形成相关的过程而形成的，或者是由于行星形成过程中吸积过程中的蒸发损失而形成的。来自地球和月球的玄武岩确实似乎具有比来自火星、灶神星和原始未分化陨石(1-4)（球粒陨石）的铁同位素成分稍重的铁同位素成分。对这些差异的解释包括创造月球的“巨大撞击”期间的蒸发（当一个火星大小的天体与年轻的地球相撞时）。然而，锂 (5) 和镁 (6) 这两种具有相当挥发性的较轻元素 (7-9) 却没有表现出这样的差异，因此蒸发不太可能作为解释。在这里，我们发现地球和月球玄武岩的硅同位素组成也明显很重。一个可能的原因是硅是地核中的轻元素之一。我们表明，硅同位素效应的方向和大小都符合基于金属和硅酸盐的键合刚度的当前理论（10）。地球和月球的块状硅酸盐的相似同位素组成与最近提出的(11)一致，即在大撞击期间存在大规模同位素平衡。我们得出的结论是，在月球形成之前，硅已经作为轻元素融入到地核中。
Small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation, or from evaporative losses during accretion as the planets were built up. Basalts from the Earth and the Moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from Mars, Vesta and primitive undifferentiated meteorites(1-4) (chondrites). Explanations for these differences have included evaporation during the 'giant impact' that created the Moon (when a Mars-sized body collided with the young Earth). However, lithium(5) and magnesium(6), lighter elements with comparable volatility(7-9), reveal no such differences, rendering evaporation unlikely as an explanation. Here we show that the silicon isotopic compositions of basaltic rocks from the Earth and the Moon are also distinctly heavy. A likely cause is that silicon is one of the light elements in the Earth's core. We show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory(10) based on the stiffness of bonding in metal and silicate. The similar isotopic composition of the bulk silicate Earth and the Moon is consistent with the recent proposal(11) that there was large-scale isotopic equilibration during the giant impact. We conclude that Si was already incorporated as a light element in the Earth's core before the Moon formed.