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Encyclopedia > Geologic time

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

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
1.2109 Ectasian  
1.4109 Calymmian
1.6109 Statherian Paleoproterozoic First complex single-celled life
1.8109 Orosirian Transition to oxygen atmosphere
2.05109 Rhyacian  
2.3109 Siderian
2.5109   Neoarchean Archaean2
2.8109 Mesoarchean
3.2109 Paleoarchean
3.6109 Eoarchean Simple single-celled life
3.8109   Hadean2,6 4.1109 - Oldest known rock;
4.4109 - Oldest known mineral;
4.57109 - 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

  • GeoWhen Database  (http://www.stratigraphy.org/geowhen/)
  • International Commission on Stratigraphy Time Scale  (http://www.stratigraphy.org/gssp.htm)

See also


  Results from FactBites:
 
Geologic time scale - Wikipedia, the free encyclopedia (1763 words)
The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth.
The table of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geologic Survey.
Different spans of time on the time scale are usually delimited by major geologic or paleontologic events, such as mass extinctions.
Fathoming Geologic Time (1252 words)
Geologic time is divided into units based on major geological and biological events, such as mountain building phases ('orogeny' in Geo-speak) or mass extinctions (relatively brief periods during which several - sometimes many - lineages die out).
Many of these blocks of time have strange, exotic-sounding names that are generally derived from the region where they were first clearly differentiated from other such blocks.
Familiarity with the sequence of the major units of geologic time will greatly enhance your understanding of the evolution of life in general and that of sharks in particular.
  More results at FactBites »

 
 

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