It is in the Archean Eon that the prokaryotes dominated the world's living things. It is earlier of the two formal divisions of Precambrian time, that is, about 4.6 billion to 541 million years ago, and the period when the life initiated on Earth.
The Archean Eon started about 4 billion years ago with the creation of Earth's crust and prolonged till the beginning of the Proterozoic Eon. The fossil proof of the primitive life forms, that is, prokaryotic microbes from the domain Archaea and bacteria appeared during this time.
During the Archean Eon, life initiated and was subjugated by the one-celled prokaryotic life forms.
The Proterozoic Eon occurred from 2.5 billion years ago to 544 million years ago. The characteristic event of the Proterozoic Eon was origin of simple eukaryotes around 1.5-1.2 billion years ago. Before evolution of eukaryotes, the living beings on earth consisted of prokaryotic life forms only. The prokaryotic life formed involved phototrophs, heterotrophic bacteria, cyanobacteria, other anoxic photosynthetic bacteria.
