The Moon forming giant impact marks the end of the main stage of Earth’s accretion and sets the stage for the subsequent evolution of our planet. The giant impact theory has been the accepted model of lunar origin for 40 years, but the parameters of the impact and the mechanisms that led to the formation of the Moon are still hotly debated. Here we review the principal geochemical observations that constrain the timing and parameters of the impact, the mechanisms of lunar formation, and the contemporaneous evolution of Earth. We discuss how chemical and isotopic studies on lunar, terrestrial and meteorite samples relate to physical models and how they can be used to differentiate between lunar origin models. In particular, we argue that the efficiency of mixing during the collision is a key test of giant impact models. A high degree of intra-impact mixing is required to explain the isotopic similarity between the Earth and Moon but, at the same time, the impact did not homogenize the whole terrestrial mantle, as isotopic signatures of pre-impact heterogeneity are preserved. We summarize the outlook for the field and highlight the key advances in both measurements and modeling needed to advance our understanding of lunar origin.

中文翻译：

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月球起源的地球化学约束和古代陆地异质性的保存

月球形成的巨大撞击标志着地球吸积主要阶段的结束，并为我们星球的后续演化奠定了基础。40年来，巨大撞击理论一直是公认的月球起源模型，但撞击参数和导致月球形成的机制仍然存在激烈争论。在这里，我们回顾了限制撞击时间和参数、月球形成机制和地球同期演化的主要地球化学观测。我们讨论了月球、地球和陨石样本的化学和同位素研究如何与物理模型相关，以及它们如何用于区分月球起源模型。特别是，我们认为碰撞过程中的混合效率是对巨型撞击模型的关键测试。需要高度的撞击内混合来解释地球和月球之间的同位素相似性，但与此同时，由于保留了撞击前异质性的同位素特征，撞击并没有使整个地球地幔均质化。我们总结了该领域的前景，并强调了促进我们对月球起源的理解所需的测量和建模方面的关键进展。