Precambrian period

Noun
1. the eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago
(synonym) Precambrian, Precambrian eon, Precambrian aeon
(hypernym) eon, aeon
(part-meronym) Proterozoic, Proterozoic eon, Proterozoic aeon

4600-570 Million Years Ago
It is through this period, which includes the Proterozoic eon and the Archean eon spanning about 2000 years each, that single celled organisms like blue-green algae and bacteria. first appeared. Towards the end of the Archean eon the first multicellular, soft bodied animals began to emerge such as jellyfish, seapens, and worms.
see list of time periods