Formation age of Earth from 129I/127I and 244Pu/238U systematics and the missing Xe

The Earth's atmosphere contains excesses of ¹²⁹Xe and ¹³⁶Xe from decay of the short-lived radionuclides ¹²⁹I and ²⁴⁴Pu, respectively. The inferred abundances of these radionuclides are substantially less than those in meteorites, nominally indicating that Earth as a planet did not form until more than 100 Myr later than the solar system as a whole, an interval rather longer than that suggested by other lines of evidence. From the comparison of elemental abundance ratios between atmospheric (assumed to approximate the total terrestrial noble gas inventory) and solar noble gases, we conclude that ∼90% of Earth's primordial Xe is missing from the atmosphere. When account is taken of the radiogenic Xe that is likely missing as well, the ¹²⁹I-²⁴⁴Pu formation interval of Earth may be reduced significantly, down to about 50-70 Myr.