Abstract
The Rb87-Sr87ages of many of the lunar rocks suggest that the fundamental differentiation took place 4.5 × 109yr ago and that remelting occurred without exchange of the rubidium and strontium with the surroundings. The Apollo A rocks are an exception to this. They appear to have acquired rubidium without all of the Sr87produced during the first aeon. Also in the remelting about half of the radiogenic leads were lost to the surroundings probably the soil by a vaporization process. We interpret these results to mean that remelting occurred in a system that was nearly closed to the surroundings and that the high early concentrations of radioactive elements in highly insulating surroundings made this possible.
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