Niobium-Zirconium Chronometry and Early Solar System Development

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Abstract
Niobium-92 (92Nb) decays to zirconium-92 (92Zr) with a half-life of 36 million years and can be used to place constraints on the site ofp-process nucleosynthesis and the timing of early solar system processes. Recent results have suggested that the initial92Nb/93Nb of the solar system was high (>10−3). We report Nb-Zr internal isochrons for the ordinary chondrite Estacado (H6) and a clast of the mesosiderite Vaca Muerta, both of which define an initial92Nb/93Nb ratio of ∼10−5. Therefore, the solar system appears to have started with a ratio of −5, which implies that Earth's initial differentiation need not have been as protracted as recently suggested.