Early Solar System Chronology

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Abstract
The short-lived radioisotope 26Al (1) has long been used as a relative chronometer of events in the early solar system. However, although much is known about its initial abundance in the early solar system, there remain doubts on applicability of 26Al chronometry, because it is not known whether it was uniformly distributed. On page 985 of this issue, Villeneuve et al. (2) report the development of new techniques that allow magnesium isotopic measurements to be made with unprecedented precision. They confirm that 26Al/27Al was indeed uniform in the early solar system to about the 10% level and find that chondrules formed in discrete events over a time period of more than 1 million years. These data are a major step forward in developing a precise and accurate chronometer, but also raise new questions about early solar system processes.