A time–scale of formation of the first solids

Abstract

We revisit an attempt to establish a unified chronology of the first ca. 20 Myr of the Solar System in the light of recent data; this period encompasses the formation of the first solids and the earliest planetary processes. We investigate the consistency of calibrations of the chronometers based on the extinct radionuclides 26Al, 53Mn and 129I with one another and with the Pb–Pb chronometer. We find the most persuasive chronology to be that based on identifying isotopic closure of the three short–lived systems in Ste Marguerite with a common event; in effect, this modifies the calibration of the I–Xe system based on Acapulco phosphate. This can be tied, in turn, to an absolute time–scale based on the Pb–Pb and Mn–Cr ages of the angrite LEW86010. The result is a common chronology (agreement between I–Xe and Mn–Cr is particularly striking), although ages derived for calcium–aluminium–rich inclusions (CAIs) are discordant. This discordancy may be explained by nuclear effects in the CAI–formation region.