Timing of accretion of the primary planetesimals in the early solar system has been investigated using short-lived (e.g., 26Al, 53Mn, 182Hf and 129I) and long-lived (e.g., 238U, 235U, 232Th and 147Sm) radionuclides. The first condensed objects in the solar system are known to be the calcium-aluminum-rich inclusions (CAIs) in chondrites (undifferentiated meteorites mainly composed of Fe- and Mg- bearing silicates), the most abundant meteorites found on Earth. The formation age of the CAIs was precisely determined by 207Pb/206Pb dating at ~4.56–4.57 Ga (Tilton 1988; Allègre et al....
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