User:Rkric2/Cambrian–Ordovician extinction event

Causes
Volcanic activity, particularly that of large igneous provinces, has been speculated to have been the cause of the environmental crisis. The emplacement of the Namaqualand–Garies dykes in South Africa has been dated to 485 Ma, the time at which the Cambrian–Ordovician extinction event occurred, although there remains no unambiguous evidence of a causal relationship between this volcanism and the biotic turnover. Anoxia and changes in sea level have also been proposed as potential causal factors. The middle Cambrian to early Ordovician is characterized by persistent elevated extinction rates that are thought to have been maintained by anoxic conditions. '''These anoxic conditions of the Cambrian are also believed to be an initiator of the Great Ordovician Biodiversification Event. '''

Effects on life
Trilobites were among the hardest hit organisms by the extinction. Shallow shelf trilobite faunas were hit particularly hard. Trilobites that inhabited the outer edges of shelf environments and slope environments, on the other hand, were minimally impacted by the event. '''Many trilobites appear to have been adapted to the anoxic conditions of the Cambrian through symbiosis with the sulfur-oxidizing bacteria. '''