"The Cambrian explosion, or less commonly Cambrian radiation, was the relatively short evolutionary event, beginning around 542 million years ago in the Cambrian Period, during which most major animal phyla appeared, as indicated by the fossil record. Lasting for about the next 20\u201325 million years, it resulted in the divergence of most modern metazoan phyla. Additionally, the event was accompanied by major diversification of other organisms."@en . . .