Geological Column


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:

NOTES to the Table








Life Forms


"Appearance of Life"


"Recent Life" (1841)

Age of Mammals

1.4% of Earth history




(1885; formerly "diluvium")

Present to
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)


(1839; formerly "alluvium")

10,000 years ago to 1.6 million years ago

Ice Ages

Homo erectus, Cro-Magnon

Large carnivores




("Late Recent"; 1833)

1.6 - 5.3

Breaching of Gibralter dam formed the Mediterranean Sea

Linking of North and South America

Whales, Apes


("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



23.7 - 36.6

Alps formed

Largest land mammals

Early primates


("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



("Old Recent"; 1874)

57.8 - 66.4

Collision of India with Eurasia

Eruption of Deccan basalts

Early horses


= "Middle Life" (1841)

Age of Reptiles

4% of Earth history

(formerly "Secondary," which also included late Paleozoic)

("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

(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


(Named "trias" for its threefold division in Germany)

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


= "Ancient Life" (1838)

7% of Earth history


(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


(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


(1870, USA only)

320 - 360

(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)




408 - 438


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


"Early Life"


88% of Earth history

The Precambrian
is not divided into
eras, periods, and epochs.

570 - 2500


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



2,500 -

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


"Beneath the Earth"

3,800 -

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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