Jurassic

I’ve always been mildly curious about the origins of the era names we use for Deep Time like Jurassic and Cretaceous. In particular, I often mix up the more recent ones. I finally laid them out spatially in a spreadsheet to try to wrap my head around it and wanted to share what I learned. At a high level, it’s pretty amazing how difficult of a problem naming eras is. Like with elements, when you discover one, you know very little about it and the name is very difficult to change even hundreds of years later.

Eons: Hadean, Archean, Proterozoic, Phanerozoic. These are all Greek and mean roughly “hellish”, “ancient”, “earlier life”, and “visible life”. Hundreds of years later we have evidence of life in the Archean, but we certainly didn’t at the time.

Most recent eras: Paleozoic, Mesozoic, Cenozoic. These are all Greek and mean roughly “old life”, “middle life”, and “new life”. They’re all subdivisions of the Phanerozoic eon, which we of course now also have evidence for life existing before.

Most recent periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quaternary. Everything before Paleogene is mostly named for the place where it was first discovered. Paleogene and Neogene are of course Greek, meaning roughly “old birth” and “new birth” (“gene” as in “genesis”). Quaternary is actually the usually quite rare English word for “fourth”, the term after primary, secondary, tertiary.

Most recent epochs: Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene (and Anthropocene, which is currently in proposal phase). These were discovered out of order and out of context and are retrospectively an incredible feat of naming. They’re all Greek, meaning roughly “old new”, “dawn new”, “few new”, “less new”, “more new”, “most new”, “all new”, and “human new”.

Eon	Era	Period	Epoch	Start (Mya)	End (Mya)	Greek Gloss	Place Name
Hadean				4567	4031	hellish
Archean				4031	2500	ancient
	Eoarchean			4031	3600	dawn ancient
	Paleoarchean			3600	3200	old ancient
	Mesoarchean			3200	2800	middle ancient
	Neoarchean			2800	2500	new ancient
Proterozoic				2500	539	earlier life
	Paleoproterozoic			2500	1600	old earlier life
		Siderian		2500	2300	iron
		Rhyacian		2300	2050	stream of lava
		Orosirian		2050	1800	mountain range
		Statherian		1800	1600	stable
	Mesoproterozoic			1600	1000	middle earlier life
		Calymmian		1600	1400	cover
		Ectasian		1400	1200	extension
		Stenian		1200	1000	narrow
	Neoproterozoic			1000	539	new earlier life
		Tonian		1000	720	stretch
		Cryogenian		720	635	cold birth
		Ediacaran		635	539		Ediacara Hills, Australia
Phanerozoic				539	0	visible life
	Paleozoic			539	252	old life
		Cambrian		539	485		Cymru (Wales)
			Terreneuvian	539	521		Terre-Neuve (Newfoundland)
			(unnamed)	521	509
			Miaolingian	509	497		Miao Ling, China
			Furongian	497	485	lotus (Mandarin)
		Ordovician		485	444		Ordovices (Celtic tribe)
		Silurian		444	419		Silures (Celtic tribe)
			Llandovery	444	433		Llandovery, Wales
			Wenlock	433	427		Wenlock Edge, England
			Ludlow	427	423		Ludlow, England
			Pridoli	423	419		Přídolí, Czechia
		Devonian		419	359		Devon, England
		Carboniferous		359	300	coal-bearing (Latin)
			Mississippian	359	323		Mississippi, USA
			Pennsylvanian	323	300		Pennsylvania, USA
		Permian		300	252		Perm, Russia
			Cisuralian	300	273		Ural Mountains (Russia/Kazakhstan)
			Guadalupian	273	260		Guadalupe Mountains, USA
			Lopingian	260	252		Loping, China
	Mesozoic			252	66	middle life
		Triassic		252	201	triad (Latin)
		Jurassic		201	145		Jura Mountains (France/Switzerland)
		Cretaceous		145	66	chalk (Latin)
	Cenozoic			66	0	new life
		Paleogene		66	23	old birth
			Paleocene	66	56	old new
			Eocene	56	33.9	dawn new
			Oligocene	33.9	23	few new
		Neogene		23	2.58	new birth
			Miocene	23	5.33	less new
			Pliocene	5.33	2.58	more new
		Quaternary		2.58	0	fourth (English)
			Pleistocene	2.58	0.012	most new
			Holocene	0.012	0	all new
			Anthropocene*	0	0	human new