Journal of the Mass Spectrometry Society of Japan

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Recently, precise noble gas analyses of many types of mantle-derived materials have proved that isotopic composition of Ne in the Earth's interior (mantle) is quite different from that of the Earth's atmosphere (²⁰Ne/²²Ne=9.8), but much similar to the solar-type composition (²⁰Ne/²²Ne-13). This observation challenges the prevailing idea that the Earth's atmosphere was simply derived from the Earth's interior, because both the atmosphere and its source (=mantle) must have identical isotopic compositions. One possibility that can account for this observation is an extensive loss of the primordial atmosphere at an early stage of the Earth's history. This model assumes a solar-type Ne both for the primordial atmosphere and the mantle, but later on, Ne in the primordial atmosphere became fractionated due to hydrodynamic escape of the atmosphere, which resulted in the “heavy” Ne isotopic composition of the present atmosphere. This paper reviews the discovery of the solar-type Ne in the Earth's interior and discuss its importance in earth and planetary sciences.

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An analytical method of stable carbon isotopic composition of individual sterols in sediment samples by gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is presented. Sterols separated from a sediment sample, are acetylated prior to GC/IRMS analysis. Replicate δ¹³C analyses of acetyl esters of 4 standard sterols revealed that the derivatization process is reproducible, with an average error (1σ) of 0.4‰±0.1‰, except for one sterol (a tri-unsaturated sterol). The original, underivatized sterol δ¹³C values were computed after an empirical correction for the carbon introduced during the acetylation. An application of the method to a marine sediment is presented with a reproducibility of 0.5‰±0.3‰.

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