http://en.wikipedia.org/wiki/Cambrian_explosion
The Cambrian explosion, or Cambrian radiation, was the relatively rapid appearance, currently dated around 542 million years ago, of most major animal phyla, as demonstrated in the fossil record. This was accompanied by major diversification of other organisms.Prior to the Cambrian explosion,most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 or 80 million years, the rate of diversification accelerated by an order of magnitude and the diversity of life began to resemble that of today.Many of the present phyla appeared during this period,with the exception of Bryozoa, which made its earliest known appearance in the Lower Ordovician.
The Cambrian explosion, or Cambrian radiation, was the relatively rapid appearance, currently dated around 542 million years ago, of most major animal phyla, as demonstrated in the fossil record. This was accompanied by major diversification of other organisms.Prior to the Cambrian explosion,most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 or 80 million years, the rate of diversification accelerated by an order of magnitude and the diversity of life began to resemble that of today.Many of the present phyla appeared during this period,with the exception of Bryozoa, which made its earliest known appearance in the Lower Ordovician.
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