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 Stratiographic 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.
Humans have an inner desire to understand and manipulate nature (agriculture, creating new breeds of animals and varieties of plants, protecting endangered species, etc.). One way that this inner nature manifests is in the desire to understand both the present and the past, and thus the study of the Tertiary sub-era (formerly period), its geology, and its life. Although students are often taught as if the scientific knowledge they are receiving is immutable and absolute, good science requires the ability to discard unworking theories and classification schemes when confronted with new facts. As the artificial division of geologic time into the periods Primary, Secondary, Tertiary, and Quaternary has proven inadequate, scientists have done away with the Primary and Secondary periods, and now the Tertiary is falling into disfavor as well.
|Cenozoic era (65-0 mya)|
|Paleocene epoch||Eocene epoch||Oligocene epoch|
|Danian | Selandian
|Ypresian | Lutetian
Bartonian | Priabonian
|Rupelian | Chattian|
|Tertiary sub-era||Quaternary sub-era|
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. Also 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 occurring 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.
The term "Tertiary" for this period was first used by Giovanni Arduino in the 1700s. 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).
- Hinton, A. C. Saving Time BlueSci Online, 2006. Retrieved September 28, 2007.
- Mayr, E. What Evolution Is. New York: Basic Books, 2001. ISBN 0-465-04425-5
- Sander, P. M., O. C. Rieppel, and H. Bucher. “New marine vertebrate fauna from the Middle Triassic of Nevada.” Journal of Paleontology, 68(3): 676-680, 1994.
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