Varas-Reus María Isabel, König Stephan, Yierpan Aierken, Lorand Jean-Pierre, Schoenberg Ronny
Isotope Geochemistry, Department of Geosciences, University of Tuebingen, Tuebingen, Germany.
Laboratoire de Planétologie et Géodynamique à Nantes, CNRS UMR 6112, Université de Nantes, Nantes, France.
Nat Geosci. 2019 Jul 2;12(9):779-782. doi: 10.1038/s41561-019-0414-7. Epub 2019 Aug 12.
The origin of Earth's volatiles has been attributed to a late addition of meteoritic material after core-mantle differentiation. The nature and consequences of this 'late veneer' are debated, but may be traced by isotopes of the highly siderophile, or iron-loving, and volatile element selenium. Here we present high-precision selenium isotope data for mantle peridotites, from double spike and hydride generation multi-collector inductively coupled plasma mass spectrometry. These data indicate that the selenium isotopic composition of peridotites is unaffected by petrological processes, such as melt depletion and melt-rock reaction, and thus a narrow range is preserved that is representative of the silicate Earth. We show that selenium isotopes record a signature of late accretion after core formation and that this signature overlaps only with that of the CI-type carbonaceous chondrites. We conclude that these isotopic constraints indicate the late veneer originated from the outer Solar System and was of lower mass than previously estimated. Thus, we suggest a late and highly concentrated delivery of volatiles enabled Earth to become habitable.
地球挥发性物质的起源被归因于地核-地幔分化之后陨石物质的后期添加。这种“后期覆层”的性质和影响存在争议，但可以通过高度亲铁（即爱铁）且具挥发性的元素硒的同位素来追踪。在此，我们通过双稀释剂和氢化物发生多接收电感耦合等离子体质谱法，给出了地幔橄榄岩的高精度硒同位素数据。这些数据表明，橄榄岩的硒同位素组成不受诸如熔体亏损和熔体-岩石反应等岩石学过程的影响，因此保留了一个代表硅酸盐地球的狭窄范围。我们表明，硒同位素记录了地核形成后后期吸积的特征，且该特征仅与CI型碳质球粒陨石的特征重叠。我们得出结论，这些同位素限制表明后期覆层起源于太阳系外部，且质量比先前估计的要低。因此，我们认为挥发性物质的后期高度集中输送使地球具备了宜居条件。
