A time-scale of formation of the first solids

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 encompass es 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 Al-26, Mn-53 and I-129 with one another and with the Pb-Pb chronometer. We find the most persuasive chronology to be that b ased on identifying isotopic closure of the three short-lived systems in St e 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-r ich inclusions (CAIs) are discordant. This discordancy may be explained by nuclear effects in the CAI-formation region.