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Encyclopedia > Geological time scale

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 4.6 billion 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.

Contents
1 Table of geologic periods
2 Graphical timeline
3 References
4 See also

Table of geologic periods

Years Ago3,5 Epoch Period/Age4 Era Eon Major Events
Present day Holocene Neogene Cenozoic Phanerozoic End of ice age and rise of modern civilization
11430 Pleistocene Extinction of many large mammals. Evolution of fully modern humans
1.81 million Pliocene  
5.33 million Miocene
23.0 million Oligocene Paleogene
37.2 million Eocene Appearance of first "modern" mammals
55.8 million Paleocene  
65.5 million*   Cretaceous Mesozoic Dinosaurs reach peak, become extinct. Primitive placental mammals
146 million Jurassic Marsupial mammals, first birds, first flowering plants
200 million Triassic First dinosaurs, Egg-laying mammals, breakup of Pangea into Gondwana and Laurasia
251 million* Permian Paleozoic Permian extinction event- 95% of life on Earth becomes extinct
299 million Carboniferous1 Pennsylvanian Abundant insects, first reptiles, coal forests
318 million Mississippian Large primitive trees, first land vertebrates
359 million Devonian First amphibians, clubmosses and horsetails appear, progymnosperms (first seed bearing plants) appear
416 million* Silurian First vascular land plants, first jawed fish
443 million* Ordovician Invertebrates dominant; first land plants
488 million* Cambrian Major diversification of life in the Cambrian explosion
542 million* Ediacaran Neoproterozoic Proterozoic2 First multi-celled animals
630 million*,7 Cryogenian Possible snowball Earth period, Rodinia begins to break up
850 million Tonian First acritarch radiation
1.0 billion Stennian Mesoproterozoic Formation of Rodinia
1.2×109 Ectasian  
1.4×109 Calymmian
1.6×109 Statherian Paleoproterozoic First complex single-celled life
1.8×109 Orosirian Transition to oxygen atmosphere
2.05×109 Rhyacian  
2.3×109 Siderian
2.5×109   Neoarchean Archaean2
2.8×109 Mesoarchean
3.2×109 Paleoarchean
3.6×109 Eoarchean Simple single-celled life
3.8×109   Hadean2,6 4.1×109 - Oldest known rock;
4.4×109 - Oldest known mineral;
4.57×109 - 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 (http://flatpebble.nceas.ucsb.edu/cgi-bin/bridge.pl?action=startScale) for an excellent time ordered list of faunal stages. Also see the article on GSSPs.
  5. The time shown in the "Years Ago" column is that of the end of the interval named beside it.
  6. Hadean was sometimes called Priscoan.
  7. 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.

Graphical timeline




References

See also


  Results from FactBites:
 
Geological Time Scale (669 words)
Think of relative time as physical subdivisions of the rock found in the Earth's stratigraphy, and absolute time as the measurements taken upon those to determine the actual time which has expired.
The overall duration and relative length of these large geologic intervals is unlikely to change much, but the precise numbers may "wiggle" a bit as a result of new data.
The time scale is depicted in its traditional form with oldest at the bottom and youngest at the top -- the present day is at the zero mark.
The Geologic Time Scale (726 words)
An era of geologic time from the beginning of the Tertiary period to the present.
An era of geologic time between the Paleozoic and the Cenozoic.
An era of geologic time, from the end of the Precambrian to the beginning of the Mesozoic.
  More results at FactBites »

 

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