ABSTRACT
High-precision noble gas data show that the Hawaiian and Icelandic mantle plume sources contain uniquely primitive neon that is composed of moderately nucleogenic neon-21 and a primordial component indistinguishable from the meteoritic occurrence of solar neon. This suggests that Earth's solar-type rare gas inventory was acquired during accretion from small planetesimals previously irradiated by solar wind from the early sun. However, nonradiogenic argon, krypton, and xenon isotopes derived from the mantle display nonsolar compositions and indicate an atmosphere-like fingerprint that is not due to recent subduction.
ABSTRACT
Two depth profiles of the osmium concentration and the 187Os/186Os isotopic ratio in the Indian Ocean showed that the osmium concentration seems to be unaltered by chemical or biological processes occuring in seawater; accordingly, osmium is conservative. These data were obtained from an experimental method that eliminated the problems related to osmium preconcentration. This method led to a new evaluation of the concentration of osmium in seawater; the mean concentration of osmium and the 187Os/186Os ratio are equal to 10.86 +/- 0.07 picograms per kilogram and 8.80 +/- 0.07, respectively. The results suggest the existence of an organocomplex that dominates the speciation of osmium in seawater.
ABSTRACT
Data from mid-ocean ridge basalt glasses indicate that the short-lived radionuclide plutonium-244 that was present during an early stage of the development of the solar system is responsible for roughly 30 percent of the fissiogenic xenon excesses in the interior of Earth today. The rest of the fissiogenic xenon can be ascribed to the spontaneous fission of still live uranium-238. This result, in combination with the refined determination of xenon-129 excesses from extinct iodine-129, implies that the accretion of Earth was finished roughly 50 million to 70 million years after solar system formation and that the atmosphere was formed by mantle degassing.
