Dates	Period	Physical/Biological Features
2,500,000,000 – 570,000,000	LATE PRECAMBRIAN	Metamorphosed sedimentary rocks, lava flows, granite; history complex and obscure; first evidence of life, calcareous algae and invertebrates.
	(Algonkian)
4,550,000,000 – 2,500,000,000	EARLY PRECAMBRIAN	Crust formed on molten earth; crystalline rocks much disturbed; history unknown.
	(Archean)