Geologic Column, by earthvisions.net at American Buddha Online Library

GEOLOGIC COLUMN

by earthvisions.net

The face of places, and their forms decay;
And that is solid earth, that once was sea;
Seas, in their turn, retreating from the shore,
Make solid land, what ocean was before.

Ovid, Metamorphoses, XV

The geological column was largely developed during the early 19th century before Darwinian evolutionary theories were used to interpret the fossils and long before radiometric techniques were developed to measure the ages of rocks. Different geological eras and periods were distinguished primarily on the basis of fossils and secondarily upon lithological and mineralogical characteristics.

For historical accounts of the development of geologists' understanding of the geological column, see the following exceptionally interesting studies:

Martin J.S. Rudwick, The Great Devonian Controversy
James Secord, The Cambrian-Silurian Controversy
David Oldroyd, The Highlands Controversy
Mott Greene, Geology in the Nineteenth Century.

NOTES to the Table

The geological column is divided according to four hierarchical levels: Eon, Era, Period, Epoch.
- A given Eon (the most comprehensive level) is composed of several Eras.
- A given Era is divided into several Periods.
- A given Period is divided into several Epochs (the smallest level).
- Epochs within the Paleozoic and Mesozoic Eras are omitted for simplicity.
Dates in parentheses after a division name indicate the date that division name was proposed.
- In some cases former names for approximately the same rocks are indicated as well.
Figures in the Dates column represent millions of years before the present.
- "2" = 2,000,000 years ago
- 4,600 = 4.6 billion years ago = 4,600,000,000
- Figures in red indicate the percent of Earth history represented by a given division.

EON	ERA	PERIOD	EPOCH	Dates	Events	Life Forms
Phanerozoic "Appearance of Life"	Cenozoic "Recent Life" (1841) Age of Mammals 1.4% of Earth history	Quaternary (1829)	Holocene (1885; formerly "diluvium")	Present to 10,000 years ago	Exploitation of natural resources Eruption of volcanoes in the Cascades	Homo sapiens Extinction of many birds and large mammals (mastodons, mammoths, saber-toothed cats)
		Quaternary (1829)	Pleistocene (1839; formerly "alluvium")	10,000 years ago to 1.6 million years ago	Ice Ages	Homo erectus, Cro-Magnon Large carnivores
		Tertiary (1759)	Pliocene ("Late Recent"; 1833)	1.6 - 5.3	Breaching of Gibralter dam formed the Mediterranean Sea Linking of North and South America	Whales, Apes
			Miocene ("Middle Recent"; 1833)	5.3 - 23.7	Himalayan Mountains formed The Mediterranean basin was a desert Formation of ice sheet on Antarctica	Large browsing mammals Abundant grasses and flowering plants
			Oligocene (1854)	23.7 - 36.6	Alps formed	Largest land mammals Early primates
			Eocene ("Dawn of the Recent"; 1833)	36.6 - 57.8	San Andreas fault formed Eruption of flood basalts to form Columbia Plateau in Oregon, Washington, and Idaho Yellowstone volcanic eruption	Mammoths
			Paleocene ("Old Recent"; 1874)	57.8 - 66.4	Collision of India with Eurasia Eruption of Deccan basalts	Early horses
	Mesozoic = "Middle Life" (1841) Age of Reptiles 4% of Earth history (formerly "Secondary," which also included late Paleozoic)	Cretaceous	("Chalky," named after the Chalk formation of southern England and the Paris basin; 1822)	66.4 - 144	Rocky Mountains formed Earliest extant sea-bed sedimentary rocks, including Chalk formation	Cretaceous - Tertiary (KT) boundary mass extinction, including dinosaurs Placental mammals
		Jurassic	(named after Jura Mountains, 1795)	144 - 208	India a separate landmass; South America separates from Africa; Tethys Sea closes to form Mediterranean; Australia and Antarctica separate	Dinosaurs reigned! 1. Bird-hipped ornithischians 2. Lizard-hipped saurischians Early birds, flowering plants
		Triassic (Named "trias" for its threefold division in Germany)	(1834)	208 - 245	Formation of Cordilleran region of North America by accretion of terranes Beginning of Pangaea breakup with opening of Atlantic Ocean between Africa and North America	Early dinosaurs and small mammals
	Paleozoic = "Ancient Life" (1838) 7% of Earth history	Permian (Named after the Perm region of Siberia, 1841)	Age of Amphibians	245 - 286	Formation of southern Appalachians from collision of North America and Africa to form Pangaea supercontinent	Mass extinction of marine and terrestrial organisms, including trilobites
		Pennsylvanian (1891, USA only)	Age of Coal Outside USA = Carboniferous, 1822	286 - 320	Shallow seas (Kaskaskia, Absaroka) cover much of North America gave rise to extensive swamps, evaporite deposits	Early coniferous plants Early reptiles
		Mississippian (1870, USA only)	Age of Coal Outside USA = Carboniferous, 1822	320 - 360		Early coniferous plants Early reptiles
		Devonian (1837; formerly "Old Red Sandstone")	Age of Fishes	360 - 408	Iapetus ocean closes; formation of northern Appalachians from collision of North America and Europe Photosynthesis increased oxygen to 21% of atmosphere	Marine mass extinction Early amphibians Winged insects Forests (evergreens) Sharks
		Silurian (1835)	Age of Fishes	408 - 438	x	Early land plants Freshwater fishes Bivalves, gastropods, corals
		Ordovician (1879)	Age of Marine Invertebrates (The Silurian, Ordovician, and Cambrian were formerly known as "Transition" rocks)	438 - 505	Ended with a mass extinction of marine invertebrates, perhaps due to an ice age	Early land animals (millipedes?) Crinoids, Bryozoans
		Cambrian (1835)		505 - 570	Shallow seas (Sauk, Tippecanoe) cover most of what is now the midwest of North America, as it lay near the equator, separated from Europe by the Iapetus Ocean	Sudden widespread appearance of early fish and shellfish, including trilobites, brachiopods, conodonts, and various predators such as cephalopoda Burgess Shale fauna
Proterozoic "Early Life"	Precambrian 88% of Earth history The Precambrian is not divided into eras, periods, and epochs.			570 - 2500 42%	Earth's north magnetic pole was near Hawaii. Photosynthesis increased oxygen from 1% to 10% of atmosphere Early supercontinent, 1.5 billion years ago. Two ice ages. Carbonate rocks deposited.	Ediacaran fauna First complex multi-cellular algae, 800 Jellyfish fossil, 670 No predators Eukaryotic life, 1.4 billion years ago
Archean "Ancient"				2,500 - 3,800	Earliest sedimentary rocks (now metamorphic gneiss and greenstone) Water vapor in atmosphere, oceans Earth cooling Oldest dated rocks 3.96 billion years ago.	First life (prokaryotic): cyanobacteria (blue-green algae), often as stromatolites
Hadean "Beneath the Earth"				3,800 - 4,600	Formation of micro-continents as islands on a sea of molten lava No oxygen in atmosphere, no life, no oceans Extensive meteorite bombardment Oldest Moon rocks, 4 to 4.6 billion years ago Formation of the Earth, 4.6 billion years ago

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