Age and Origin of the Moon

The age and origin of the moon have been studied with the use of the recently developed short-lived hafnium-tungsten chronometer ( 182 Hf- 182 W, half-life of nine million years). The tungsten isotopic compositions of 21 lunar samples range from chondritic to slightly radiogenic (ɛ W = −0.50 ± 0.60 to +6.75 ± 0.42). This heterogeneity may have been inherited from material excavated from Earth and the putative impactor, but it is more likely the result of late radioactive decay within the moon itself; in this case, the moon formed 4.52 to 4.50 billion years ago, and its mantle has since remained poorly mixed.