Cambrian explosion
The Cambrian explosion was the relatively rapid appearance around of most major animal phyla as demonstrated in the fossil record, and many more phyla now extinct. 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, although they did not resemble the species of today.