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Title: When did the Moon-forming giant impact happen?
Plain: Different lunar rocks and minerals give formation ages from about 4.51 to about 4.35 billion years ago. Whether the Moon formed early and was later remelted, or formed late, is disputed.
Precise: The oldest lunar zircons give ages near 4.46 to 4.51 Ga, whereas many ferroan anorthosites and lunar magma-ocean model ages cluster near 4.35 Ga. Determine the age of the Moon-forming impact and whether the 4.35 Ga cluster records formation or a later tidally driven remelting of an older Moon. An answer is an impact age with uncertainty below about 2e7 yr consistent with lunar and terrestrial Hf-W, Sm-Nd and U-Pb chronometers.
Settled by: Concordant high-precision dating of the oldest lunar crust and zircons, including newly returned samples, tested against tidal-heating models of the early Moon.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: contested
Status note: Nimmo, Kleine and Morbidelli (Nature 2024, https://doi.org/10.1038/s41586-024-08231-0) argued the $4.35\,\mathrm{Ga}$ ages reflect tidally driven remelting of an older Moon.
Posed since: (empty)