The iodine-plutonium-xenon age of the Moon-Earth system revisited

Iodine-plutonium-xenon isotope systematics have been used to re-evaluate time constraints on the early evolution of the Earth-atmosphere system and, by inference, on the Moon-forming event. Two extinct radionuclides (I-129, T(1/)2 = 15.6 Ma and Pu-244, T(1/)2 = 180 Ma) have produced radiogenic Xe-129 and fissiogenic Xe131-136, respectively, within the Earth, the related isotope fingerprints of which are seen in the compositions of mantle and atmospheric Xe. Recent studies of Archaean rocks suggest that xenon atoms have been lost from the Earth's atmosphere and isotopically fractionated during long periods of geological time, until at least the end of the Archaean eon. Here, we build a model that takes into account these results. Correction for Xe loss permits the computation of new closure ages for the Earth's atmosphere that are in agreement with those computed for mantle Xe. The corrected Xe formation interval for the Earth-atmosphere system is 40(-10)(+20) Ma after the beginning of Solar System formation. This time interval may represent a lower limit for the age of the Moon-forming impact.