Chronology of Asteroid Accretion and Differentiation

The study of short-lived, now extinct radionuclides offers constraints on the duration of planetesimal formation and on other processes and events, which took place in the early solar system. The relative chronometers based on the decay of 53Mn to 53Cr (T1/2 = 3.7 m.y.) and of 26Al to 26Mg (T1/2 = 0.73 m.y.) provide an adequate time resolution of at least 1 m.y. A calibration of these relative chronometers with an absolute Pb-Pb chronometer permits converting relative ages into absolute ages. Using reasonable assumptions, an absolute timescale for events in the early solar system can be constructed. Based on the studies of these isotope systems in various meteorites, we estimated the formation time of the first high-temperature condensates (Ca-Al-rich meteorite inclusions) in the solar system, inferred constraints on the duration of planetesimal accretion, calculated the time of planetary melting, mantle, and core formation, and constrained the timing of igneous processes and thermal metamorphism within planetesimals.