Noble gases in an Hawaiian xenolith

THE noble gas record in meteorites and lunar samples has been the subject of many investigations aimed at determining their age, the history of their exposure to cosmic rays and to the solar wind, and the early chronology of events in the Solar System (see review in ref. 1). Information on the latter is contained primarily in the isotopes of xenon, where the decay products of extinct 129 I and 244 Pu provide a record of the synthesis of elements and the early history of planetary solids (see review in ref. 2). The occurrence of radiogenic xenon in CO 2 well gas from Harding County, New Mexico is the only clear evidence that extinct radioactivities were present in the early history of the Earth 3,4 , but the suggestion that this radiogenic xenon had been brought near the Earth's surface in hot magmas was not confirmed by recent analyses of xenon in lava rock from this region 5 .