Precambrian Overview The Precambrian Eon is made up of three separate sub-type eons; the Hadean Eon (4.6 - 4.0 BYA), the Archean Eon (4.0 - 2.5 BYA), and the Proterozoic Eon (2.5 BYA - 542 MYA).
At the beginning of the Precambrian Eon and Hadean eon, Earth was molten lava. Around the end of the Hadean eon the first rain appeared which lead to the first sign of life in the Archean eon. The first sign of life was in a fossil dated 3.5 BYA and it was a Stromatolite. At the end of the Archean eon the first photosynthesizing organisms began to develop and produce oxygen which lead to the beginning of the Proterozoic eon. Many life forms at this time were not able to absorb oxygen and went extinct, while others evolved into multicellular organisms. The end and beginning of the Proterozoic eon was brought on by glaciation.