EON	ARCHEAN	ARCHEAN	ARCHEAN	ARCHEAN
ERA	Eoarchean	Paleoarchean	Mesoarchean	Neoarchean
PERIOD	none	none	none	none
EPOCH	none	none	none	none
YEARS	4 - 3.6 bya	3.6 - 3.2 bya	3.2 - 2.8 bya	2.8 - 2.5 bya

EON	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC	PROTEROZOIC
ERA	Paleoproterozoic	Paleoproterozoic	Paleoproterozoic	Paleoproterozoic	Mesoproterozoic	Mesoproterozoic	Mesoproterozoic	Neoproterozoic	Neoproterozoic	Neoproterozoic
PERIOD	Siderian	Rhyacian	Orosirian	Statherian	Calymmian	Ectasian	Stenian	Tonian	Cryogenian	Ediacaran
EPOCH	none	none	none	none	none	none	none	none	none	none
YEARS	2.5 - 2.3 bya	2.3 - 2.05 bya	2.05 - 1.8 bya	1.8 - 1.6 bya	1.6 - 1.4 bya	1.4 - 1.2 bya	1.2 - 1.0 bya	1.0 - .850 bya	.850 - .635 bya	.635 - .542 bya

"bya" means billions of years ago

The Earth's geological ages are classified as follows:

4 eons, each of which lasts approximately a billion years.
10 eras, each lasting about several hundred million years.
22 periods, which last about a hundred million years each. Only the proterozoic and the phanerozoic eons are divided into periods.
34 epochs, each lasting tens of millions of years. Only the phanerozoic eon is divided into epochs.