Encyclopedia > Geologic Timescale

  Article Content

Geologic timescale

Redirected from Geologic Timescale

A timeline of Geologic periods.

(not shown to scale)

Years Ago3,6 Epoch Period/Age4,5 Era Eon Major Events
Present day Holocene Quaternary Cenozoic Phanerozoic  
10,000 Pleistocene Extinction of many large mammals. Evolution of fully modern humans
1.6 million Pliocene Tertiary Neogene  
5 million Miocene
23 million Oligocene Paleogene
38 million Eocene
55 million Paleocene
64.3 million*   Cretaceous Mesozoic Dinosaurs reach peak, become extinct. Primitive placental mammals
146 million Jurassic Marsupial mammals, first birds, first flowering plants[?]
208 million Triassic First dinosaurs, Egg-laying mammals
251.1 million* Permian Paleozoic Permian extinction event- 95% of life on Earth becomes extinct
286 million Carboniferous1 Pennsylvanian Abundant insects, first reptiles, coal forests
325 million Mississippian Large primitive trees
360 million Devonian First amphibians, clubmosses and horsetails appear, progymnosperms[?] (first seed bearing plants) appear
408.5 million* Silurian First land plant fossils
443.5 million* Ordovician Invertebrates dominant
490 million* Cambrian Major diversification of life in the Cambrian explosion
545 million* Neoproterozoic2 Proterozoic Precambrian First multi-celled animals
900 million Mesoproterozoic[?]  
1,600 million Paleoproterozoic First Complex single-celled life
2,500 million Archaean Simple single-celled life
3,800 million Hadean Formation of Earth

1) In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods

2) Discoveries in the past quarter century have substantially changed the view of geologic and paleontologic events immediately prior to the Cambrian. The nomenclature has not stabilized. The term Neoproterozoic is used here, but other writers might equally well have used one or more of the terms 'Ediacarian', 'Vendian', 'Varangian', 'Precambrian', 'Protocambrian', 'Eocambrian', or might have extended the Cambrian further back in time. All of these terms are usually treated as a subset of the Proterozoic rather than a period between the Paleozoic and the Proterozoic.

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. All dates given are for the end of the epoch in question.

4) Paleontologists often refer to faunal stages rather than geologic Periods. The Stage Nomenclature is quite complex. See http://flatpebble.nceas.ucsb.edu/public/harland for an excellent time ordered list of faunal stages. Also see the article on GSSPs.

5) In common usage the Tertiary-Quaternary and Paleogene-Neogene-Quaternary Periods are treated as equivalents to the Mesozoic and Paleozoic Periods. The term 'Period|Age' (e.g. 'Neogene Period|Age') is sometimes used instead of 'Period'.

6) The time shown in the "Years Ago" column is that of the end of the Epoch in the "Epoch" column.

See also:



All Wikipedia text is available under the terms of the GNU Free Documentation License

 
  Search Encyclopedia

Search over one million articles, find something about almost anything!
 
 
  
  Featured Article
O.J. Simpson

... being used to satisfy judgments, so Simpson was able to continue much of his lifestyle based on his NFL pension. Since this trial Simpson has been largely regarded as ...