Precambrian

adj. of the earliest geological period

The Precambrian (Pre-Cambrian) is an informal name for the supereon comprising the eons of the geologic timescale that came before the current Phanerozoic eon. It spans from the formation of Earth around 4500 Ma (million years ago) to the evolution of abundant macroscopic hard-shelled animals, which marked the beginning of the Cambrian, the first period of the first era of the Phanerozoic eon, some 542 Ma.
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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 eon, Precambrian aeon, Precambrian period
(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

precambrian
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