Asteroid breakup linked to the Great Ordovician Biodiversification Event

Abstract

The rise and diversification of shelled invertebrate life in the early Phanerozoic eon occurred in two major stages. During the first stage (termed as the Cambrian explosion), a large number of new phyla appeared over a short time interval ∼540 Myr ago. Biodiversity at the family, genus and species level, however, remained low until the second stage marked by the Great Ordovician Biodiversification Event in the Middle Ordovician period^1,2,3. Although this event represents the most intense phase of species radiation during the Palaeozoic era and led to irreversible changes in the biological make-up of Earth’s seafloors, the causes of this event remain elusive. Here, we show that the onset of the major phase of biodiversification ∼470 Myr ago coincides with the disruption in the asteroid belt of the L-chondrite parent body—the largest documented asteroid breakup event during the past few billion years^4,5. The precise coincidence between these two events is established by bed-by-bed records of extraterrestrial chromite, osmium isotopes and invertebrate fossils in Middle Ordovician strata in Baltoscandia and China. We argue that frequent impacts on Earth of kilometre-sized asteroids—supported by abundant Middle Ordovician fossil meteorites and impact craters⁶—accelerated the biodiversification process.