A rain of ordinary chondritic meteorites in the early Ordovician

Forty fossil meteorites with a total original mass of ∼7.7 kg have been recovered in the first systematic search for fossil meteorites, pursued in an active quarry in Lower Ordovician (480 Ma) marine limestone in southern Sweden. The meteorites represent at least 12 different falls over a seafloor area of ∼6000 m2 during ≤1.75 Myr, making the quarry one of the most meteorite dense areas known in the world. Geochemical analyses of relict chromite grains indicate that all or most of the meteorites are ordinary chondrites and probably L chondrites. Mechanisms for meteorite delivery from the asteroid belt to Earth were the same 480 Ma as today, however, the flux was one to two orders of magnitude higher, most likely reflecting the disruption of the L chondrite parent body at about that time. This is a major event in late solar-system history, which may also have led to an enhanced flux of asteroids to Earth during ∼30 Myr.