Question: what kinds of life forms were dominant during the precambrian era

title: Precambrian
text: Neoproterozoic : The youngest geologic era of the Proterozoic Eon , from the Cambrian Period lower boundary ( 541 Ma ) back to 1000 Ma . The Neoproterozoic corresponds to Precambrian Z rocks of older North American geology . Ediacaran : The youngest geologic period within the Neoproterozoic Era . The `` 2012 Geologic Time Scale '' dates it from 541 to 635 Ma . In this period the Ediacaran fauna appeared . Cryogenian : The middle period in the Neoproterozoic Era : 635 - 720 Ma . Tonian : the earliest period of the Neoproterozoic Era : 720 - 1000 Ma .