More than 99 percent of all species, amounting to over five billion species,[12] that ever lived on Earth are estimated to be extinct.

The Cambrian explosion or Cambrian radiation[1] was the relatively short evolutionary event, beginning around 541 million years ago in the Cambrian period, during which most major animal phyla appeared, as indicated by the fossil record.[2][3] Lasting for about the next 20[4][5]–25[6][7] million years, it resulted in the divergence of most modern metazoan phyla.[8] Additionally, the event was accompanied by major diversification of other organisms.[note 1] Prior to the Cambrian explosion,[note 2] most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 to 80 million years, the rate of diversification accelerated by an order of magnitude[note 3] and the diversity of life began to resemble that of today.