Globally synchronous meteorite rain during the Middle Ordovician

Abstract

A Middle Ordovician breakup of a L-chondrite asteroid parent body (LCPB) has been suggested to have facilitated both an ice age and a major radiation of marine life. This hypothesis, however, is debated as Baltic data show an offset between the events on Earth and the LCPB-associated meteorite rain. Here, we present the first SIMS UPb date (465.9 ± 3.3 Ma) from zircons in a bentonite from the Wangjiawan region, South China. We pinpoint the events in space, the LCPB breakup, to have occurred at 466.09 ± 3.3 Ma, and further estimate that the extraordinarily intense micrometeorite rain lasted 2.58 ± 0.27 Myr with an intensity of ∼2.9 × 10⁴ grains/m²/Myr. This suggests that the influx intensity would likely have been too minimal to have had any discernable effect on either climate or biodiversity levels. Our U/Pb age from South China thus implies that the LCPB breakup was a synchronous global event, but was too insignificant in intensity, and further occurred after both the major climatic shift and biological radiation, indicating no relationship between them.