Tertiary

{{Short description|Former term for the geologic period from 65 million to 2.58 million years ago}}
{{About|the geological term|other uses|Tertiary (disambiguation)}}
{{Infobox geologic timespan
| name                         = Tertiary
| color                        = Tertiary
| time_start                   = 66.0
| time_end                     = 2.6
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<!--Chronology-->  
| timeline                     = Cenozoic
| formerly_part_of             =
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<!--Etymology-->
| chrono_name                  =
| strat_name                   =
| name_formality               = Informal
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<!--Usage Information--> 
| celestial_body               = earth
| usage                        = Regional(?)
| timescales_used              = [[International Commission on Stratigraphy|ICS]] Time Scale (formerly)
| formerly_used_by             = ICS
| not_used_by                  =
<!--Definition-->
| chrono_unit                  = Period
| strat_unit                   = System
| proposed_by                  =
| type_section                 =
| timespan_formality           = Informal
| lower_boundary_def           = K-Pg extinction event
| lower_gssp_location          = None
| lower_gssp_accept_date       = N/A
| upper_boundary_def           = Beginning of the [[Quaternary]] glaciation
| upper_gssp_location          = None
| upper_gssp_accept_date       = N/A
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}}
'''Tertiary''' ({{IPAc-en|ˈ|t|ɜːr|.|ʃ|ə|.|r|i|,_|ˈ|t|ɜː|r|.|ʃ|i|ˌ|ɛr|.|i}} {{respell|TUR|shə|ree|,_|TUR|shee|err|ee}})<ref>{{cite news |last= |first= |date= |title=tertiary [ tur-shee-er-ee, tur-shuh-ree ] |url=https://www.dictionary.com/browse/tertiary |work=Dictionary.com Unabridged |location= |access-date=5 January 2022}}</ref> is an obsolete term for the [[Period (geology)|geologic period]] from 66&nbsp;million to 2.6&nbsp;million years ago. 
The period began with the demise of the non-[[bird|avian]] [[dinosaur]]s in the [[Cretaceous–Paleogene extinction event]], at the start of the [[Cenozoic|Cenozoic Era]], and extended to the beginning of the [[Quaternary glaciation]] at the end of the [[Pliocene|Pliocene Epoch]]. The time span covered by the Tertiary has no exact equivalent in the current [[geologic time]] system, but it is essentially the merged [[Paleogene]] and [[Neogene]] periods, which are informally called the Early Tertiary and the Late Tertiary, respectively.

==Historical use of the term==
The term Tertiary was first used by [[Giovanni Arduino (geologist)|Giovanni Arduino]] during the mid-18th century. He classified geologic time into primitive (or primary), secondary, and tertiary periods based on observations of geology in [[Northern Italy]].<ref>{{cite book |first=Carl O. |last=Dunbar |title=Historical Geology |edition=2nd |year=1964 |publisher=John Wiley & Sons |location=New York, NY |page=352}}</ref> Later a fourth period, the [[Quaternary]], was applied.

In the early development of the study of geology, the periods were thought by [[scriptural geologist]]s to correspond to the Biblical narrative, the rocks of the Tertiary being thought to be associated with the [[Flood myth|Great Flood]].<ref name="Rudwick">{{cite book |author-link=Martin J. S. Rudwick |author=Rudwick, M. J. S. |year=1992 |title=Scenes from Deep Time: Early Pictorial Representations of the Prehistoric World |publisher=[[University of Chicago Press]] |chapter-url=https://books.google.com/books?id=eM0xUqbjzs0C |chapter=Except |isbn=9780226731056 |via=Google Books}}</ref>

In 1833, [[Charles Lyell]] incorporated a Tertiary Period into his own, far more detailed system of classification, based on [[fossil]] [[mollusk]]s he collected in Italy and Sicily in 1828-1829. He subdivided the Tertiary Period into four epochs according to the percentage of fossil mollusks resembling modern species found in those [[stratum|strata]]. He used [[Greek language|Greek]] names: Eocene, Miocene, Older Pliocene, and Newer Pliocene.<ref>{{cite journal |last1=Berggren |first1=William A. |title=The Cenozoic Era: Lyellian (chrono)stratigraphy and nomenclatural reform at the millennium |journal=Geological Society, London, Special Publications |date=1998 |volume=143 |issue=1 |pages=111–132 |doi=10.1144/GSL.SP.1998.143.01.10|bibcode=1998GSLSP.143..111B |s2cid=44668464 |citeseerx=10.1.1.488.5133 }}</ref>

Although these divisions seemed adequate for the region to which the designations were originally applied (parts of the [[Alps]] and plains of Italy), when the same system was later extended to other parts of Europe and to America, it proved to be inapplicable. Therefore, the use of mollusks was abandoned from the definition and the epochs were renamed and redefined.{{Citation needed|date=February 2024|reason=Citation needed for the entire above section, where none are provided}}

For much of the time during which the term 'Tertiary' was in formal use, it referred to the span of time between 65 and 1.8 million years ago. The end date of the Cretaceous and the start date of the Quaternary were subsequently redefined at c. 66 and 2.6 million years ago respectively.{{Citation needed|date=February 2024|reason=Citation needed for the entire above section, where none are provided}}

==Modern equivalents==
The Tertiary period lies between the [[Mesozoic|Mesozoic Era]] and the [[Quaternary|Quaternary Period]], although it is no longer recognized as a formal unit by the [[International Commission on Stratigraphy]].{{Citation needed|date=February 2024|reason=Citation needed for the entire above section, where none are provided}}

The span of the Tertiary is subdivided into the [[Paleocene]] (66–56&nbsp;million years [[Before Present|BP]]), the [[Eocene]] (56–33.9&nbsp;million years BP), the [[Oligocene]] (33–23.9&nbsp;million years BP), the [[Miocene]] (23–5.3&nbsp;million years BP) and the [[Pliocene]] (5.3–2.6&nbsp;million years BP), extending to the first stage of the [[Pleistocene]], the [[Gelasian]] Stage.<ref name="International Stratigraphic Chart">{{cite web |title=International Chronostratigraphic Chart |url=http://stratigraphy.org/ICSchart/ChronostratChart2013-01.pdf |publisher=International Commission on Stratigraphy |author=Cohen, K. M. |author2=Finney, S. |author3=Gibbard, P. L. |date=January 2013}}</ref><ref>{{cite book |author1=Ogg, James G. |author2=Gradstein, F. M. |author3=Gradstein, Felix M. |title=A Geologic Time Scale 2004 |url=https://archive.org/details/geologictimescal2004grad |url-access=limited |publisher=Cambridge University Press |location=Cambridge, UK |year=2004 |isbn=978-0-521-78142-8 |page=[https://archive.org/details/geologictimescal2004grad/page/n66 45] |chapter=1: Chronostratigraphy: Linking time and rock}}</ref><ref>{{cite web |title=On the Geologic Time Scale 2008 |url=http://www.stratigraphy.org/bak/gts2008.pdf |author1=Gradstein, Felix M. |author2=Ogg, James G. |author3=van&nbsp;Kranendonk, Martin |publisher=International Commission on Stratigraphy |access-date=18 December 2013 |page=5}}</ref><ref>{{cite book |author1=Vandenberghe, N. |author2=Hilgen, F.J. |author3=Speijer, R.P. |title=The Geologic Time Scale 2012 |year=2012 |publisher=Elsevier |location=Amsterdam |isbn=978-0-44-459425-9 |page=856 |edition=1st |editor1=Gradstein, Felix M. |editor2=Ogg, James G. |editor3=Schmitz, Mark D. |editor4=Ogg, Gabi M. |chapter=28: The Paleogene period |doi=10.1016/B978-0-444-59425-9.00028-7 |s2cid=129821669 |url=https://lirias.kuleuven.be/handle/123456789/320727}}</ref>

==References==
{{Reflist}}

==External links==
{{wiktionary|Tertiary|tertiary}}
* {{Cite EB1911|wstitle=Tertiary|short=x}}

{{Authority control}}

[[Category:Cenozoic geochronology]]