information:classification, structural:expansion, structural:reformatting
Hypotheses about cause

Explaining an event from 250 million years ago is inherently difficult, with much of the evidence on land eroded or deeply buried, while the spreading seafloor is completely recycled over 200 million years, leaving no useful indications beneath the ocean.

Yet, scientists have gathered significant evidence for causes, and several mechanisms have been proposed. The proposals include both catastrophic and gradual processes (similar to those theorized for the Cretaceous–Paleogene extinction event, but with much less current consensus).

Any hypothesis about the cause must explain the selectivity of the event, which affected organisms with calcium carbonate skeletons most severely; the long period (4 to 6 million years) before recovery started, and the minimal extent of biological mineralization (despite inorganic carbonates being deposited) once the recovery began.