Abstract
Recent geochemical and geophysical data from the Moon enable a revision of earlier interpretations regarding lunar origin, structure and bulk composition. Earth and Moon show many similarities among their isotopic compositions, but they have evolved in totally dissimilar ways, probably related to the deficiency of water and volatile elements in the Moon as well as the vast differences in size and internal pressure. Some global geochemical differences from the Earth such as volatile depletion based on K/U ratios have been established. However, all current lunar samples come from differentiated regions, making the establishment of a bulk composition more reliant on bulk geophysical properties or isotopic similarities; it remains unclear how the latter arose or relate to whole Moon composition. The lack of fractionation effects among the refractory and super-refractory elements indicates that the proto-lunar material seems unlikely to have been vaporized while the presence of volatile elements may place lower limits on proto-lunar temperatures. The apparent lack of geochemical evidence of an impacting body enables other possible impactors, such as comets, to be considered. Although the origin of the Moon remains currently unknown, it is generally believed that the Moon originated as the result of a giant impact on the Earth.
Highlights
Despite decades of research following the samples returned by the Apollo Missions, the Moon remains an enigma with currently little consensus on lunar composition or on the origin of our satellite
The average composition of the feldspathic crust remains somewhat uncertain, it clearly requires a large-scale fractionation that is more consistent with a lunar magma ocean than, for example, construction of the crust by serial intrusion and local differentiation of discrete batches of magmas produced by smaller degrees of melting of a primitive lunar mantle (e.g., Walker 1983; Solomon and Longhi 1977), which might produce compositional differences among elements such as the rare earth elements (REE)
The Earth and Moon show many similarities among their isotopic compositions, they have evolved in totally dissimilar ways, probably related to the deficiency of water and volatile elements in the Moon
Summary
Despite decades of research following the samples returned by the Apollo Missions, the Moon remains an enigma with currently little consensus on lunar composition or on the origin of our satellite. For the past 25 years, scientists have accepted that the Moon formed as a result of the low-angle collision between the Earth and another body about the size of Mars. Such a scenario solved many problems but predicted that the Moon should contain a significant amount of material from the impactor. It has been generally held, based mostly on meteorite evidence that possible Moonforming impactors would likely possess isotopic ratios (notably in oxygen) that differ from those of Earth.
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