Abstract:
Patterson (1956) established that the age of Earth is close to that of meteorites. Over the last 20 years, workers argued for younger age for core differentiation based on Pb-Pb model ages and tungsten isotopic data and for gas retention based on I-Xe modeling. However, disagreement is abundant, and the young age of Earth has not been widely accepted. In this work, I examine all radiogenic noble gases in the atmosphere and use a model-independent approach and total inversion to show that (1) the Xe-closure age of Earth is 109 +/- 23 million years younger than the formation of meteorite Bjurbole (~4560 Ma) and (2) all radiogenic components of noble gases in the atmosphere can be quantitatively accounted for by production and degassing ~60% of the bulk silicate earth. The agreement between the 129I-129Xe clock and 244Pu-238U-136Xe-134Xe-132Xe-131Xe clock suggests that the volatility of iodine does not affect the 129I-129Xe clock. Earth's Xe-closure age is 4.45 +/- 0.02 Ga, consistent with the model age of Pb and the 146Sm-142Nd, 147Sm-143Nd and 182Hf-182W systematics. On the basis of the consistency of these ages, 4.45 +/- 0.02 Ga probably represents the time when the last Martian-sized planetesimal hit Earth and reinitialized the global clocks.