Cambrian explosion of life: theBig Bang in metazoan evolution

Despite the protracted history of life on earth spanning well over 3.8 Ga, fossil record of the Precambrian (> 543 Ma) largely documents only microscopic life. The mostly simple Precambrian life forms were followed by a sudden explosive radiation of multicellular animals at the turn of the Cambrian period (543–490 Ma) between 530 and 520 Ma ago, when almost two-thirds of the animal phyla make their dramatic appearance in the fossil record. This unusual and amazing burst of macroevolutionary change is called the Cambrian explosion