Three-dimensional, spheroidal structures of carbon atoms, Cn (n>40), can be made with 12 pentagons and (n/2)-10 hexagons. Kroto et al. (1985) have shown that the molecule C60, called Buckminsterfullerene, is especially stable and that soot might be made of nuclei of Cn shells. Inert gas atoms might become trapped in such structures when they form by the condensation of carbon from a gas phase. Niemeyer and Marti (1981) have shown that trapping in condensing carbon occurs and is attended by mass fractionation. The hypothesis of gas trapping in Cn-shells and/or in soot particles derived from them might explain the thermal release patterns of trapped inert gases in acid-resistant residues of carbonaceous chondrites up to at least 1000¿ C. The hypothesis predicts ''graphitization'' of the acid-resistant residues with the gas-release.