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Pressure-dependent isotopic composition of iron alloys

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Science  29 Apr 2016:
Vol. 352, Issue 6285, pp. 580-582
DOI: 10.1126/science.aad9945

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Iron isotopes constrain core chemistry

The overall composition of Earth's core is an important constraint on the chemistry and evolution of our planet's interior. A longstanding problem has been determining the minor element contribution to its predominately iron-nickel alloy. Based on the iron isotope fractionation of various iron alloys with pressure, Shahar et al. find that carbon and hydrogen are probably not primary components of the core. The fractionation occurs at the high pressures of core formation, suggesting that the stable iron isotope ratios of Earth are a new and independent constraint on core composition.

Science, this issue p. 580

Abstract

Our current understanding of Earth’s core formation is limited by the fact that this profound event is far removed from us physically and temporally. The composition of the iron metal in the core was a result of the conditions of its formation, which has important implications for our planet’s geochemical evolution and physical history. We present experimental and theoretical evidence for the effect of pressure on iron isotopic composition, which we found to vary according to the alloy tested (FeO, FeHx, or Fe3C versus pure Fe). These results suggest that hydrogen or carbon is not the major light-element component in the core. The pressure dependence of iron isotopic composition provides an independent constraint on Earth’s core composition.

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