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Geologic timescale

The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. When used in formal writing, specific geological and historical periods and events are capitalized. Some examples: the Silurian Period, the Ice Age, the Neolithic, the Archean; however, when not specific, some historical events remain uncapitalized, as in ice ages.

The Earth is thought by geologists to be 4570 million years old. The geologic or "deep" time of Earth's past has been organized into various periods according to events which took place in each period.


Table of geologic periods

Years Ago3,6
Epoch Period4 Era Eon Major Events
Present day Holocene Neogene5 Cenozoic Phanerozoic End of ice age and rise of modern civilization
0.011430 0.00013 Pleistocene Extinction of many large mammals; Evolution of fully modern humans
1.806 0.005 * Pliocene  
5.332 0.005 * Miocene
23.03 0.05 * Oligocene Paleogene5
33.9 0.1 * Eocene Appearance of first "modern" mammals
55.8 0.2 * Paleocene  
65.5 0.3 *   Cretaceous Mesozoic Dinosaurs reach peak, become extinct. Primitive placental mammals
145.5 4.0 Jurassic Marsupial mammals, first birds, first flowering plants
199.6 0.6 Triassic First dinosaurs, egg-laying mammals, breakup of Pangea into Gondwana and Laurasia
251.0 0.4 * Permian Paleozoic Permian extinction event- 95% of life on Earth becomes extinct
299.0 0.8 * Carboniferous1 Pennsylvanian Abundant insects, first reptiles, coal forests
318.1 1.3 * Mississippian Large primitive trees, first land vertebrates
359.2 2.5 * Devonian First amphibians, clubmosses and horsetails appear, progymnosperms (first seed bearing plants) appear
416.0 2.8 * Silurian First vascular land plants, first jawed fish
443.7 1.5 * Ordovician Invertebrates dominant; first land plants
488.3 1.7 * Cambrian Major diversification of life in the Cambrian Explosion
542.0 1.0 * Ediacaran Neoproterozoic Proterozoic2 First multi-celled animals
630 +5/-30 *,8 Cryogenian Possible snowball Earth period, Rodinia begins to break up
850 0 9 Tonian First acritarch radiation
1000 0 9 Stennian Mesoproterozoic Formation of Rodinia
1200 0 9 Ectasian  
1400 0 9 Calymmian
1600 0 9 Statherian Paleoproterozoic First complex single-celled life
1800 0 9 Orosirian Transition to oxygen atmosphere
2050 0 9 Rhyacian  
2300 0 9 Siderian
2500 0 9   Neoarchean Archaean2 Stabilization of most modern cratons, possible mantle overturn event
2800 0 9 Mesoarchean  
3200 0 9 Paleoarchean First known oxygen producing bacteria
3600 0 9 Eoarchean Simple single-celled life
3800   Hadean2,7 4100 MYA - Oldest known rock;
4400 MYA - Oldest known mineral;
4570 MYA - Formation of Earth
  1. In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods.
  2. The Proterozoic, Archean and Hadean are often collectively referred to as Precambrian Time, and sometimes also as the Cryptozoic.
  3. Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where we would most like to have them. Dates with an * are radiometrically determined based on internationally agreed to GSSPs. The dates quoted above are according to the International Commission on Stratigraphy 2004 time scale. All dates given are for the end of the interval in question.
  4. Paleontologists often refer to faunal stages rather than geologic Periods. The Stage Nomenclature is quite complex. See Harland for an excellent time ordered list of faunal stages. Also see the article on GSSPs.
  5. Historically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. However, the International Commission on Stratigraphy has recently decided to stop using the terms Quaternary and Tertiary as part of the formal nomenclature.
  6. The time shown in the "Years Ago" column is that of the end of the interval named beside it.
  7. Hadean is not a formal eon. It was sometimes called Priscoan.
  8. The GSSP for the base of the Ediacaran, ratified in 2004, is a climatic/geochemical marker rather than biostratigraphic. It represents the end of a widespread glaciation event.
  9. Defined by absolute age (Global Standard Stratigraphic Age ).

Graphical timeline


See also

External link

Last updated: 08-24-2005 06:45:32