Abstract The orbital elements of the solar system’s ancient asteroid families are highly dispersed, recording the last dynamical chaos in its history. However, dynamics alone cannot precisely date this when this terminal chaos occurred. Instead, we can precisely date the collisions triggered by such dynamical rearrangement to constrain this event. On planets, erosion, volcanism, and crustal recycling have removed almost all trace of rocks older than 4 Ga, erasing the archive of early solar system history. In contrast, the meteorite record generated by asteroid collisions represents a separate and more complete archive of the solar system’s early dynamical evolution. Here we build a record of in situ ordinary chondrite meteorite apatite U-Pb ages, sensitive to collisions that induce parent-body break-up events. We show that the U-Pb records of strongly shocked and weakly shocked meteorites are distinct. The U-Pb ages of weakly shocked meteorites record the decline of radiogenic heating in asteroidal bodies. Meanwhile, shocked meteorite ages record major collisions. All sampled ordinary chondrite bodies record collisions that occurred 4480 ± 20 Ma million years ago. No further multi-parent-body clusters of shock ages are found in this record until the very recent events that brought the meteorites to Earth. These ages constrain that the last date of major dynamical chaos to modify the orbital elements of asteroids occurred at around 4480 Ma. This date is relatively late in solar system history, possibly representing the timing of an orbital instability of the giant planets.
Walton et al. (Wed,) studied this question.