Cerium-Nd isotope evidence for an incompatible element depleted Moon.

The Moon is the best example of a planetary body that has formed after a collisional impact event. A better understanding of its bulk composition can provide new constraints on its building blocks and can help clarifying whether the Earth-Moon system is chondritic in its lithophile trace element composition or not. A recent study revealed that Earth has a higher 142 Nd/ 144 Nd composition than would be expected from pure s-/r-process variations [1] . This can be explained, if Earth has accreted from material with a higher p-process component [1] , or if Earth has lost an early enriched reservoir [2] . To provide new constraints whether and possibly when Earth has lost an enriched reservoir, we have applied the long-lived 138 La- 138 Ce and 147 Sm- 143 Nd systems to 30 lunar samples, covering the most important lunar petrological rock types (low and high Ti basalts, KREEPs, and ferroan anorthosites). Present day and initial Ce-Nd lunar isotope arrays do not intersect the chondritic value, arguing for a non-chondritic composition of the Moon. Trace element and isotope modelling of lunar magma ocean crystallization [3] further imply that a slightly depleted bulk Moon composition is required to match the observed data, although the degree of depletion must be smaller compared to previous estimates of a super-chondritic Earth composition [2] . When comparing previously reported Ce-Nd isotope data of 3.3±0.25 Ga Archean rocks from the Kaapvaal [4] and