Tertiary

The Tertiary period was once prominent as a major division of the geologic timescale, designating the time from the end of the Cretaceous period about 65 million years ago to the start of the Quaternary period about 1.6 million years ago. While its use has been widespread and continues, the International Commission on Stratigraphy no longer endorses this term as part of the formal stratigraphic nomenclature. Instead the Paleogene and Neogene periods are recommended as the primary subdivisions of the Cenozoic era. The Quaternary likewise has been subsumed into the Neogene. When the term Tertiary is used now, it is generally as a "sub-era" rather than a "period" of geologic time (Hinton 2006).

In common usage, the Tertiary has included five geologic epochs—the Paleocene, Eocene, Oligocene, Miocene, and Pliocene. The Tertiary covers roughly the time span between the demise of the dinosaurs and beginning of the most recent ice age.

Cenozoic era (65-0 mya)
Paleogene	Neogene      Quaternary

Tertiary sub-era
Paleogene period
Paleocene epoch	Eocene epoch	Oligocene epoch
Danian | Selandian Thanetian	Ypresian | Lutetian Bartonian | Priabonian	Rupelian | Chattian

Tertiary sub-era			Quaternary sub-era
Neogene period
Miocene		Pliocene	Pleistocene	Holocene
Aquitanian	Burdigalian	Zanclean	Early
Langhian	Serravallian	Piacenzian	Middle
Tortonian	Messinian	Gelasian	Late

Description

The end of the Cretaceous period and the beginning of the Tertiary period was marked by a mass extinction event known as the Cretaceous-Tertiary extinction event. As known as the K-T extinction event, it was a period of massive extinction of species that occurred about 65.5 million years ago. Many forms of life perished, encompassing approximately 50 percent of all plant and animal families, the most conspicuous being the non-avian dinosaurs. Some recognize this mass extinction now as occuring at the Cretaceous-Paleogene boundary rather than the K-T boundary (Hinton 2006).

At the start of the Tertiary, we begin to see the first large mammals and primitive primates. Soon, at the start of the Eocene, the first modern mammals began to appear, and within a relatively brief period of time most modern mammal orders appeared. Reptiles were replaced as the dominant animals by mammals during the Tertiary. Fossils reveal that early during the Tertiary there also were already modern representatives of birds, reptiles, fish, and amphibians. The earliest recognizable hominoid relatives of humans, Proconsul and Australopithecus, appeared during the Tertiary as well. Modern families of flowering plants evolved, while marine invertebrates and non-mammal marine vertebrates experienced only modest evolution.

Continental drift was modest, although Gondwana separated completely. Mayr (2001) noted that in the early Tertiary (40 million years ago), there was a broad land connection between Europe and North America across the North Atlantic. This allowed an active faunal exchange, as evidenced by the discovery of a large fossil fauna of Tertiary camels in North America, connecting modern day camels in the Old World with their close relatives the llamas in South America. Towards the end of the Tertiary, South America also was connected to North America. Antarctica—which was already separate—drifted to its current position over the South Pole. Climates during the Tertiary slowly cooled, starting off in the Paleocene with tropical-to-moderate worldwide temperatures and ending up with extensive glaciations at the end of the period.

Name

The term "Tertiary" for this period was first used by Giovanni Arduino in the 1700's. He classified geologic time into primitive (or primary), secondary, and tertiary periods based on observations of geology in northern Italy. Later the Quaternary was added as a fourth period.

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. These designations, albeit adequate for the areas originally applied, were not universally applicable. Therefore, later the use of mollusks was abandoned from the definition and the epochs were renamed and redefined.

The Primary and Secondary periods have been done away with as periods, and the Tertiary and Quaternary are now generally placed at the level of "sub-era" when used. There is little reference in literature to intervals of time of "sub-era" and thus some consider it logical to also remove the name Tertiary from geologic time (Hinton 2006).

References

ISBN links support NWE through referral fees

• Hinton, A. C. 2006. Saving Time. BlueSci Online. (accessed December 3, 2006).
• Mayr, E. 2001. What Evolution Is. New York: Basic Books. ISBN 0-465-04425-5.

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