Defining the age of the Moon has proven to be an elusive task because it requires reliably dating lunar samples using radiometric isotopic systems that record fractionation of parent and daughter elements during events that are petrologically associated with planet formation. Crystallization of the magma ocean is the only event that unambiguously meets this criterion because it probably occurred within tens of millions of years of Moon formation. There are three dateable crystallization products of the magma ocean: mafic mantle cumulates, felsic crustal cumulates, and late-stage crystallization products known as urKREEP (uniform residuum K, rare earth elements, and P). Although ages for these materials in the literature span 200 million years, there is a preponderance of reliable ages around 4.35 billion years recorded in all three lunar rock types. This age is also observed in many secondary crustal rocks, indicating that they were produced contemporaneously (within uncertainty of the ages), possibly during crystallization and overturn of the magma ocean. ▪The duration of planet formation is key information in understanding the mechanisms by which the terrestrial planets formed.▪Ages of the oldest lunar rocks range widely, reflecting either the duration of Moon formation or disturbed ages caused by impact metamorphism.▪Ages determined for compositionally distinct crust and mantle materials produced by lunar magma ocean differentiation cluster near 4.35 Gyr.▪The repeated occurrence of 4.35 Gyr ages implies that Moon formation occurred late in Solar System history, likely by giant impact into Earth.

中文翻译：

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月球形成的演变年表


事实证明，定义月球的年龄是一项难以捉摸的任务，因为它需要使用辐射同位素系统可靠地测定月球样本的年代，该系统记录了在岩石学上与行星形成相关的事件中母元素和子元素的分馏。岩浆海洋的结晶是唯一明确满足这一标准的事件，因为它可能发生在月球形成的数千万年内。岩浆海洋有三种可测年结晶产物：镁铁质地幔累积物、长英质地壳累积物和称为 urKREEP（均匀残余物 K、稀土元素和 P）的晚期结晶产物。尽管文献中这些材料的年龄跨越 2 亿年，但在所有三种月球岩石类型中，记录的可靠年龄都在 43.5 亿年左右。在许多次生地壳岩石中也观察到这个年龄，表明它们是同时期产生的（在年龄的不确定性范围内），可能是在岩浆海洋的结晶和翻转过程中。▪行星形成的持续时间是理解类地行星形成机制的关键信息。▪最古老的月球岩石的年龄范围很广，反映了月球形成的持续时间或撞击变质作用引起的扰动年龄。▪确定的年龄是由 4.35 Gyr 附近的月球岩浆海洋分化团产生的成分不同的地壳和地幔物质。▪4.35 Gyr 年龄的重复出现意味着月球形成发生在太阳系的历史，很可能是由于巨大的撞击而进入地球。