Age of a lunar anorthosite.
The crystallization age of an Apollo 15 anorthosite rock, 15415,9, returned from the lunar highlands has been measured to be (4.09 +/- 0.19) x 10(9) years. The primitive lunar crust must have been formed in the first 300 to 400 x 10(6) years. The results give some credence to the hypothesis that the primitive lunar surface was molten and large-scale fractional crystallization occurred in the early history of the moon.