Niobium-Zirconium Chronometry and Early Solar System Development

Abstract

Niobium-92 ( 92 Nb) decays to zirconium-92 ( 92 Zr) with a half-life of 36 million years and can be used to place constraints on the site of p -process nucleosynthesis and the timing of early solar system processes. Recent results have suggested that the initial 92 Nb/ 93 Nb 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 initial 92 Nb/ 93 Nb ratio of ∼10 −5 . Therefore, the solar system appears to have started with a ratio of <3 × 10 −5 , which implies that Earth's initial differentiation need not have been as protracted as recently suggested.