The term Tertiary was first used byGiovanni Arduino during the mid-18th century. He classified geologic time into primitive (or primary), secondary, and tertiary periods based on observations of geology inNorthern Italy.[2] Later a fourth period, theQuaternary, was applied.
In the early development of the study of geology, the periods were thought byscriptural geologists to correspond to the Biblical narrative, the rocks of the Tertiary being thought to be associated with theGreat Flood.[3]
In 1833,Charles Lyell incorporated a Tertiary Period into his own, far more detailed system of classification, based onfossilmollusks 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 thosestrata. He usedGreek names: Eocene, Miocene, Older Pliocene, and Newer Pliocene.[4]
Although these divisions seemed adequate for the region to which the designations were originally applied (parts of theAlps 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]
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.[5][6]
In 1989, theInternational Commission on Stratigraphy (ICS) eliminated the use of "Tertiary" on their stratigraphic charts, instead dividing this timespan into thePaleogene andNeogene periods[6] (terms which had been coined over a century earlier in the 1850s by Austrian geologistMoritz Hörnes[7]), which in previous stratigraphic charts were treated as subdivisions of the Tertiary.[6] In 2004, the ICS considered the Neogene to also include the entireQuaternary period, thus making the Neogene span until the present,[8] but this was not widely followed and the ICS later restored the Quaternary to full period status by 2009.[6] In 2006 it was remarked that despite the ICS elimination of the term over a decade earlier, at that time, "Tertiary" was still more common than Paleogene and Neogene.[8]
The Tertiary period lies between theMesozoic Era and theQuaternary Period, although it is no longer recognized as a formal unit by the International Commission on Stratigraphy.[5][6]
The span of the Tertiary is subdivided into thePaleocene (66–56 million yearsBP), theEocene (56–33.9 million years BP), theOligocene (33.9–23.04 million years BP), theMiocene (23.04–5.333 million years BP) and thePliocene (5.333–2.58 million years BP), extending to the first stage of thePleistocene, theGelasian Stage.[9][10][11][12]
^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.ISBN978-0-521-78142-8.
^Gradstein, Felix M.; Ogg, James G.; van Kranendonk, Martin."On the Geologic Time Scale 2008"(PDF). International Commission on Stratigraphy. p. 5. Retrieved18 December 2013.
