RARE-GAS SYSTEMATICS IN POPPING ROCK - ISOTOPIC AND ELEMENTAL COMPOSITIONS IN THE UPPER-MANTLE

New experimental data on the isotopic variations of neon, argon, and x enon in a popping rock imply that the Ar-40/Ar-36 ratio of the upper m antle is less than 44,000 and that the Xe-129/Xe-130 ratio is less tha n 8.2. The elemental abundance pattern of rare gases is chondritic-lik e and is quite distinct from the solar pattern. These data imply that Earth accreted from planetesimals that probably underwent a transforma tion of their rare gas budget from solar- to chondritic-like, leaving the isotopic composition unchanged from the solar pattern.