The I-Pu-Xe age of the Moon-Earth system revisited

From iodine-plutonium-xenon isotope systematics, we re-evaluate time constraints on the early evolution of the Earth-atmosphere system and, by inference, on the Moon-forming event. Two extinct radioactivites (129 I, T 1/2 = 15.6 Ma, and 244 Pu, T 1/2 = 80 Ma) have produced radiogenic 129 Xe and fissiogenic 131-136 Xe, respectively, within the Earth, which related isotope fingerprints are seen in the compositions of mantle and atmospheric Xe. Recent studies of Archean 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 Archean eon. Here we build a model that takes into account these results. Correction for Xe loss permits to compute new closure ages for the Earth's atmosphere that are in agreement with those computed for mantle Xe. The minimum Xe formation interval for the Earth-atmosphere is 40-10 +20 Ma after start of solar system formation, which may also date the Moon-forming impact.