Homogeneous Distribution of 26Al in the Solar System from the Mg Isotopic Composition of Chondrules

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Science  21 Aug 2009:
Vol. 325, Issue 5943, pp. 985-988
DOI: 10.1126/science.1173907

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The timing of the formation of the first solids in the solar system remains poorly constrained. Micrometer-scale, high-precision magnesium (Mg) isotopic analyses demonstrate that Earth, refractory inclusions, and chondrules from primitive meteorites formed from a reservoir in which short-lived aluminum-26 (26Al) and Mg isotopes were homogeneously distributed at ±10%. This level of homogeneity validates the use of 26Al as a precise chronometer for early solar system events. High-precision chondrule 26Al isochrons show that several distinct chondrule melting events took place from ~1.2 million years (My) to ~4 My after the first solids condensed from the solar nebula, with peaks between ~1.5 and ~3 My, and that chondrule precursors formed as early as 0.87-0.16+0.19 My after.

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