State Key Laboratory of Geological Processes and Minerals Resources, China University of Geosciences, Beijing, 100083, China.
Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, 230026, China.
Nat Commun. 2021 Jan 12;12(1):294. doi: 10.1038/s41467-020-20525-1.
Earth's habitability is closely tied to its late-stage accretion, during which impactors delivered the majority of life-essential volatiles. However, the nature of these final building blocks remains poorly constrained. Nickel (Ni) can be a useful tracer in characterizing this accretion as most Ni in the bulk silicate Earth (BSE) comes from the late-stage impactors. Here, we apply Ni stable isotope analysis to a large number of meteorites and terrestrial rocks, and find that the BSE has a lighter Ni isotopic composition compared to chondrites. Using first-principles calculations based on density functional theory, we show that core-mantle differentiation cannot produce the observed light Ni isotopic composition of the BSE. Rather, the sub-chondritic Ni isotopic signature was established during Earth's late-stage accretion, probably through the Moon-forming giant impact. We propose that a highly reduced sulfide-rich, Mercury-like body, whose mantle is characterized by light Ni isotopic composition, collided with and merged into the proto-Earth during the Moon-forming giant impact, producing the sub-chondritic Ni isotopic signature of the BSE, while delivering sulfur and probably other volatiles to the Earth.
地球的宜居性与其晚期吸积密切相关，在此期间，撞击体带来了大部分生命必需的挥发物。然而，这些最终构建块的性质仍然受到很大限制。镍（Ni）可以作为特征描述这种吸积的有用示踪剂，因为大部分地幔硅酸盐地球（BSE）中的 Ni 都来自晚期撞击体。在这里，我们对大量陨石和地球岩石进行了 Ni 稳定同位素分析，发现 BSE 的 Ni 同位素组成比球粒陨石轻。利用基于密度泛函理论的第一性原理计算，我们表明核心-地幔分异不能产生 BSE 观测到的轻 Ni 同位素组成。相反，亚球粒陨石的 Ni 同位素特征是在地球晚期吸积过程中建立的，可能是通过形成月球的巨大撞击。我们提出，一个富含硫化物、类似水星的物体，其地幔具有轻的 Ni 同位素组成，在形成月球的巨大撞击中与原地球碰撞并合并，产生了 BSE 的亚球粒陨石 Ni 同位素特征，同时向地球输送了硫和可能其他挥发物。
