Department of Earth Sciences, Parks Road, Oxford OX1 3PR, UK.
Nature. 2010 Jun 10;465(7299):767-70. doi: 10.1038/nature09072.
The meaning of the age of the Earth defined by lead isotopes has long been unclear. Recently it has been proposed that the age of the Earth deduced from lead isotopes reflects volatile loss to space at the time of the Moon-forming giant impact rather than partitioning into metallic liquids during protracted core formation. Here we show that lead partitioning into liquid iron depends strongly on carbon content and that, given a content of approximately 0.2% carbon, experimental and isotopic data both provide evidence of strong partitioning of lead into the core throughout the Earth's accretion. Earlier conclusions that lead is weakly partitioned into iron arose from the use of carbon-saturated (about 5% C) iron alloys. The lead isotopic age of the Earth is therefore consistent with partitioning into the core and with no significant late losses of moderately volatile elements to space during the giant impact.
长期以来，用铅同位素定义的地球年龄的意义一直不清楚。最近有人提出，从铅同位素推断出的地球年龄反映了在月球形成的巨大撞击时挥发物向太空的损失，而不是在长期的核心形成过程中分配到金属液体中。在这里，我们表明，铅在液态铁中的分配强烈依赖于碳的含量，并且，鉴于大约 0.2%的碳含量，实验和同位素数据都为在整个地球的吸积过程中，铅强烈地分配到核心提供了证据。早些时候关于铅在铁中弱分配的结论来自于对含碳饱和（约 5% C）的铁合金的使用。因此，地球的铅同位素年龄与分配到核心的情况一致，并且在巨大撞击期间，没有中等挥发性元素大量向太空损失的情况。
