Distinct oxygen isotope compositions of the Earth and Moon
Distinct oxygen isotope compositions of the Earth and Moon
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DOI：
10.1038/s41561-020-0550-0
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发表时间：
2020-04-01
影响因子：
18.3
通讯作者：
Shearer, Charles K.
中科院分区：
文献类型：
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作者：
Cano, Erick J.;Sharp, Zachary D.;Shearer, Charles K.
阿波罗返回样本揭示的地球和月球几乎相同的氧同位素组成对月球形成模型来说是一个具有挑战性的限制。对于解释这一观察结果的巨大撞击情景，要么地球和月球的前身具有相同的氧同位素值，要么在撞击事件后两个天体发生了广泛的同质化。在这里，我们对一系列月球岩性进行了高精度氧同位素分析，并表明地球和月球实际上具有明显不同的氧同位素组成。月球样本的氧同位素值与岩性相关，我们认为这种差异可以通过撞击产生的同位素轻蒸气与早期月球岩浆海洋最外层之间的混合来解释。我们的数据表明，来自月幔深处的样本与地球相比同位素重，其同位素成分最能代表原月球撞击星“忒伊亚”。我们的研究结果表明，忒伊亚和地球不同的氧同位素组成并没有因月球形成的影响而完全均质化，从而提供了定量证据，证明忒伊亚形成时可能比地球距离太阳更远。高精度测量表明，地球和月球具有不同的氧同位素组成。这意味着原地球及其撞击物具有不同的氧同位素组成，这些组成并未因月球形成的撞击而完全均质化。
The virtually identical oxygen isotope compositions of the Earth and Moon revealed by Apollo return samples have been a challenging constraint for lunar formation models. For a giant impact scenario to explain this observation, either the precursors to the Earth and Moon had identical oxygen isotope values or extensive homogenization of the two bodies occurred following the impact event. Here we present high-precision oxygen isotope analyses of a range of lunar lithologies and show that the Earth and Moon in fact have distinctly different oxygen isotope compositions. Oxygen isotope values of lunar samples correlate with lithology, and we propose that the differences can be explained by mixing between isotopically light vapour, generated by the impact, and the outermost portion of the early lunar magma ocean. Our data suggest that samples derived from the deep lunar mantle, which are isotopically heavy compared to Earth, have isotopic compositions that are most representative of the proto-lunar impactor 'Theia'. Our findings imply that the distinct oxygen isotope compositions of Theia and Earth were not completely homogenized by the Moon-forming impact, thus providing quantitative evidence that Theia could have formed farther from the Sun than did Earth.High-precision measurements suggest that the Earth and Moon have distinct oxygen isotope compositions. This implies distinct oxygen isotopic compositions of the proto-Earth and its impactor that were not fully homogenized by the Moon-forming impact.