Cambrian-Ordovician extinction event
From Tardis Wiki, the free Doctor Who reference
The Cambrian-Ordovician extinction event was a mass extinction event which marked the transition from the Cambrian to Ordovician. It was caused by a change in sea level, flooding portions of the two super-continents of the Cambrian era, Laurentia and Baltica and Gondwana. (PROSE: Prehistory Repeating Itself [+]Loading...["Prehistory Repeating Itself (feature)"])
