Tertiary

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Events of the Cenozoic
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N. Amer. prairie expands[1]
First Antarctic permanent ice-sheets[2]
Holocene begins 11.5 ka ago
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An approximate timescale of key Cenozoic events.
Axis scale: Ma before present.

Tertiary is an officially deprecated but still widely used term for a geologic period from 65 million to 1.806 million years ago, a time span that lies between the superseded Secondary period and the Quaternary. The Tertiary is no longer recognized as a formal unit by the International Commission on Stratigraphy,[4] its traditional span being divided between the Paleogene and Neogene Periods and the first stage of the Pleistocene of the Cenozoic Era.

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 spanned to the beginning of the Quaternary glaciation at the end of the Pliocene Epoch. The Tertiary also included the early Pleistocene.

Historical use of the term[edit]

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.[5] Later a fourth period, the Quaternary, was applied.

In the early development of the study of geology, the periods were thought to correspond to the Biblical narrative, the rocks of the Tertiary being thought to be associated with the Great Flood.[6]

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.

Geological events[edit]

Tectonic activity continued as Gondwana finally split completely apart, and India collided with the Eurasian plate.

South America was connected to North America toward the end of the Tertiary, and this resulted in climate changes in the mid to late Tertiary.

Antarctica — which was already separate — drifted to its current position over the South Pole during this era. Widespread volcanic activity was prevalent.

Climate[edit]

Climates during the Tertiary slowly cooled, starting off in the Paleocene with tropical-to-moderate worldwide temperatures and ending before the first extensive glaciation at the start of the Quaternary.

References[edit]

  1. ^ Retallack, G. J. (1997). "Neogene Expansion of the North American Prairie". PALAIOS 12 (4): 380–390. doi:10.2307/3515337. JSTOR 3515337. 
  2. ^ Zachos, J. C.; Kump, L. R. (2005). "Carbon cycle feedbacks and the initiation of Antarctic glaciation in the earliest Oligocene". Global and Planetary Change 47 (1): 51–66. Bibcode:2005GPC....47...51Z. doi:10.1016/j.gloplacha.2005.01.001. 
  3. ^ Krijgsman, W.; Garcés, M.; Langereis, C. G.; Daams, R.; Van Dam, J.; Van Der Meulen, A. J.; Agustí, J.; Cabrera, L. (1996). "A new chronology for the middle to late Miocene continental record in Spain". Earth and Planetary Science Letters 142 (3-4): 367–380. Bibcode:1996E&PSL.142..367K. doi:10.1016/0012-821X(96)00109-4. 
  4. ^ International Stratigraphic Chart[dead link]
  5. ^ Carl O. Dunbar, Historical Geology, 2nd ed. (1964), John Wiley & Sons, New York, p. 352
  6. ^ Rudwick, M.J.S (1992): Scenes from Deep Time: Early Pictorial Representations of the Prehistoric World, University of Chicago Press, 280 pages. Except from Google Books