Tertiary (/ˈtɜːr.ʃə.ri, ˈtɜːr.ʃiˌɛr.i/ TUR-shə-ree, TUR-shee-err-ee)[1] is a widely used, but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start of the Cenozoic Era, and extended to the beginning of the Quaternary glaciation at the end of the 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 Lower Tertiary and the Upper Tertiary, respectively.

Events of the Cenozoic
An approximate timescale showing subdivisions of the Cenozoic Era.
Axis scale: millions of years before present.

Historical use of the term

The term Tertiary was first used by 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.[2] Later a fourth period, the Quaternary, was applied.

In the early development of the study of geology, the periods were thought by scriptural geologists to correspond to the Biblical narrative, the rocks of the Tertiary being thought to be associated with the Great Flood.[3]

In 1828, Charles Lyell incorporated a Tertiary Period into his own, far more detailed system of classification. He subdivided the Tertiary Period into four epochs according to the percentage of fossil mollusks resembling modern species found in those strata. He used Greek names: Eocene, Miocene, Older Pliocene, and Newer Pliocene.

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.

Modern equivalents

The Tertiary's time span lies between the Mesozoic Era and the Quaternary, although no longer recognized as a formal unit by the International Commission on Stratigraphy.

The span of the Tertiary is subdivided into the Paleocene Epoch (56–66 million years BP), the Eocene Epoch (33.9–56 million years BP), the Oligocene Epoch (23–33.9 million years BP), the Miocene Epoch (5.3–23 million years BP) and the Pliocene Epoch (2.6–5.3 million years BP), extending to the first stage of the Pleistocene Epoch, the Gelasian stage.[4][5][6][7]


  1. https://www.dictionary.com/browse/tertiary
  2. Dunbar, Carl O. (1964). Historical Geology (2nd ed.). New York, NY: John Wiley & Sons. p. 352.
  3. Rudwick, M.J.S. (1992). "Except". Scenes from Deep Time: Early Pictorial Representations of the Prehistoric World. University of Chicago Press via Google Books.
  4. Cohen, K.M.; Finney, S.; Gibbard, P. L. (January 2013). "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
  5. Ogg, James G.; Gradstein, F.M.; Gradstein, Felix M. (2004). "1: Chronostratigraphy: Linking time and rock". A Geologic Time Scale 2004. Cambridge, UK: Cambridge University Press. p. 45. ISBN 978-0-521-78142-8.
  6. Gradstein, Felix M.; Ogg, James G.; van Kranendonk, Martin. "On the Geologic Time Scale 2008" (PDF). International Commission on Stratigraphy. p. 5. Retrieved 18 December 2013.CS1 maint: multiple names: authors list (link)
  7. Vandenberghe, N.; Hilgen, F.J.; Speijer, R.P. (2012). "28: The Paleogene period". In Gradstein, Felix M.; Ogg, James G.; Schmitz, Mark D.; Ogg, Gabi M. (eds.). The Geologic Time Scale 2012 (1st ed.). Amsterdam: Elsevier. p. 856. doi:10.1016/B978-0-444-59425-9.00028-7. ISBN 978-0-44-459425-9.
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