Deep-mantle krypton reveals Earth’s early accretion of carbonaceous matter
Deep-mantle krypton reveals Earth’s early accretion of carbonaceous matter
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深地幔氪揭示了地球早期碳质物质的吸积
DOI：
10.1038/s41586-021-04092-z
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发表时间：
2021
期刊：
影响因子：
64.8
通讯作者：
Graham, David W.
中科院分区：
文献类型：
--
作者：
Péron, Sandrine;Mukhopadhyay, Sujoy;Kurz, Mark D.;Graham, David W.
确定碳、氮和水何时何地被输送到地球，是了解地球等宜居行星起源的一个基本目标。然而，不稳定的地球输送仍然存在争议，，，-。尽管普遍存在的大气污染阻碍了分析工作，但氪同位素由于其在来源、-之间的巨大同位素差异，提供了对挥发性输送的洞察。在这里，我们介绍了加拉帕戈斯和冰岛地幔深处的整套氪同位素，它们具有最原始的氦、霓和钨同位素组成、-。除了86Kr外，氪的同位素组成类似于球粒陨石和大气氪的混合物。这些结果表明，原始地球早期积聚了碳质物质，并排除了水动力损失和深部或浅部地幔放气的任何组合来解释大气惰性气体。令人意外的是，与碳质陨石的平均成分相比，深部地幔源富中子86Kr存在亏损，这表明存在核合成异常。虽然与碳质陨石相比，地球上富中子同位素的相对贫化已经被证明是一系列难熔元素的相对贫化，但我们的观察表明，对于挥发性元素来说，这种贫化是这样的。这一发现表明，挥发性元素和难熔元素的吸积同时发生，氪记录了不止一种物质(可能包括外太阳系行星体)伴随的非太阳挥发物质的吸积。
Establishing when, and from where, carbon, nitrogen and water were delivered to Earth is a fundamental objective in understanding the origin of habitable planets such as Earth. Yet, volatile delivery to Earth remains controversial, , , –. Krypton isotopes provide insights on volatile delivery owing to their substantial isotopic variations among sources, , , –, although pervasive atmospheric contamination has hampered analytical efforts. Here we present the full suite of krypton isotopes from the deep mantle of the Galápagos and Iceland plumes, which have the most primitive helium, neon and tungsten isotopic compositions, , , , –. Except for86Kr, the krypton isotopic compositions are similar to a mixture of chondritic and atmospheric krypton. These results suggest early accretion of carbonaceous material by proto-Earth and rule out any combination of hydrodynamic loss with outgassing of the deep or shallow mantle to explain atmospheric noble gases. Unexpectedly, the deep-mantle sources have a deficit in the neutron-rich86Kr relative to the average composition of carbonaceous meteorites, which suggests a nucleosynthetic anomaly. Although the relative depletion of neutron-rich isotopes on Earth compared with carbonaceous meteorites has been documented for a range of refractory elements,,, our observations suggest such a depletion for a volatile element. This finding indicates that accretion of volatile and refractory elements occurred simultaneously, with krypton recording concomitant accretion of non-solar volatiles from more than one type of material, possibly including outer Solar System planetesimals.
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