IV. ERAS
                   

In all of prehistory, there are only ten named well-defined eras.

Most of the exciting ideas many of us have about ancient earth come from the three most recent eras. These all fall within the most recent aeon, the Phanerozoic, that spans the last half a billion years. Labelled 8 to 10 below, these eras are the ones most commonly referred to in popular writings.

The first seven named eras are within the Archean and Proterozoic aeons, and practically they are limited to academic or geological references.

The earliest (Hadean) aeon currently does not possess characteristics or events that allow for subdivision into eras. Future studies of lunar geology may provide new information that would amend this.

The eras are numbered 1 to 10 below, but these numbers are only for ease of using the table. Other columns give starting and ending dates in millions of years ago (mya), and key points about the era.

	(00) (=Panhadean eras)	4600	4000	Molten volcanic earth. Asteroid bombardment. Lunar separation.	.
	01 Eoarchaean	4000	3700	“Ancient Dawn”. Surface magma coexists with early seas. Abiotic genesis. Oldest rocks form Canadian Shield, Zircons. Raw iron, sulphur.
	02 Aleoarchaean	3700	3200	Supercontinent-1 Vaalbara/Ur forms/breaks. CO2/CH4 air. Oxygen 1% air begins.
	03 Mesoarchaean	3200	2700	Early life – non-nucleated single-cells
	04 Neoarchaean	2700	2400	Supercontinent-2 Kenorland forms/breaks.
	05 Paleoproterozoic	2400	1500	Supercontinent-3 Nuna forms/breaks. Glacial-1, 2400 to 2100 mya, Huronian glacial. Supercontinent Laurentia forms/breaks
	06 Mesoproterozoic	1500	750	Supercontinent-4, Rodinia forms/ breaks, Glacial-2: Cryogenian, "snowball earth", 850 to 630 mya.
	07 Neoproterozoic	750	542	Supercontinent-5 Vendia forms/breaks
	08 Paleozoic	542	250	Cambrian “explosion” of visible life. Notable Periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Supercontinent-6 Gondwana-Pangaea forms. Glacial-3 (Andean-Saharan, 460 to 420 mya). Glacial-4 (Karoo,360 to 260 mya). Ordovician extinction (marine, anoxic cold deep-water). Permian extinction (massive magma extrusion).
	09 Mesozoic	250	65	Time of reptiles, dinosaurs. Notable Periods: Triassic, Jurassic, Cretaceous. Supercontinent-6 Gondwana-Pangaea breaks. Tertiary extinction (meteorites).
	10 Cenozoic	65	0	Time of mammals. Latest of 3 periods: Quaternary. Latest 2 of 7 Epochs: Pleistocene 2.6 mya to 12,500 yra, includes Paleolithic (Old Stone Age); Glacial-5 (the Quaternary, 2.6 to 0 mya with four recent ice chrons at regular 140,000 yr intervals; Holocene 12,500 yra to now, Neolithic, agriculture, civilizations