Ordovician meteor event

The Ordovician meteor event was a dramatic increase in the rate at which L chondrite meteorites fell to Earth during the Middle Ordovician period, about million years ago, lasting for about 40 million years. This rate increase is indicated by abundant fossil L chondrite meteorites in a quarry in Sweden and enhanced concentrations of ordinary chondritic chromite grains in sedimentary rocks from this time.H. Haack et al. Meteorite, asteroidal, and theoretical constraints on the 500-Ma disruption of the L chondrite parent body, Icarus, Vol. 119, p. 182 (1996).

According to a 2019 study, this temporary increase in the impact rate could have been caused by the destruction of the L chondrite parent body that was in diameter and orbited in the asteroid belt between Mars and Jupiter. This occurred around million years ago, having scattered fragments into Earth-crossing orbits, a chronology which is also supported by shock ages in numerous L chondrite meteorites that fall to Earth today.

It has been speculated that this influx contributed to, or possibly even instigated, the Great Ordovician Biodiversification Event, although this has been questioned.An extraterrestrial trigger for the mid-Ordovician ice age: Dust from the breakup of the L-chondrite parent body, Birger Schmitz et al, AAAS Science Advances, 18 Sep 2019: Vol. 5, no. 9, eaax4184; DOI: 10.1126/sciadv.aax4184, accessed 2019-10-09

A 2024 study found that all of 21 studied craters from this event were at the time within 30° of the equator. Impactors directly from the asteroid belt would be expected to produce a random distribution of craters, so this suggests that the event may have been caused by an asteroid that passed within Earth's Roche limit and broke up into a ring system, material from which then deorbited and formed the craters. It is also speculated that the shading of Earth by this ring may have contributed to the Hirnantian glaciation.

Possible craters

Ordovician meteor event

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