Difference between revisions of "Paleogene" - New World Encyclopedia
Rick Swarts (talk | contribs) |
Rick Swarts (talk | contribs) |
||
| Line 1: | Line 1: | ||
| − | '''Paleogene''' (alternatively '''Palaeogene''') | + | The '''Paleogene''' (alternatively '''Palaeogene''') period is a major division of the [[geologic time scale]] and the first of two periods that mark our current era, the [[Cenozoic]]. The Paleogene began 65.5 ± 0.3 million years ago (mya) and ended 23.03 ± 0.05 mya. The Paleogene begins at the end of the [[Cretaceous]] period and is followed by the [[Neogene]] period, the current and final period of the Cenozoic. The Paleogene encompasses the [[Paleocene]], [[Eocene]], and [[Oligocene]] epochs. |
| − | + | The [[Tertiary]] was one prominent as the period that began at the end of the [[Cretaceous]] period. While its use has been widespread and continues, the International Commission on Stratigraphy no longer endorses this term as part of the [http://www.stratigraphy.org/gssp.htm formal stratigraphic nomenclature]. When the term Tertiary is used now, it is generally as a "sub-era," which includes the Paleogene and part of the Neogene, rather than a "period" of geologic time (Hinton 2006). The [[Quaternary]] likewise has been subsumed into the Neogene and considered a "sub-era," although this remains quite controversial; the change has been opposed by many geologists, botanists, zoologists, and others (Hinton 2006). | |
| − | + | The end of the Cretaceous period and the beginning of the Paleogene (originally Tertiary) was marked by a [[mass extinction|mass extinction event]] known as the [[mass extinction#Cretaceous-Tertiary extinction event|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, including most [[dinosaur]]s. Some recognize this mass extinction now as occurring at the Cretaceous-Paleogene boundary rather than the K-T boundary (Hinton 2006). | |
| + | |||
| + | Another major phenomena during the Paleogene was one of the most significant periods of global change during the Cenozoic, the ''Paleocene-Eocene Thermal Maximum''. | ||
| + | |||
| + | Lasting 42 million years, the Paleogene period is most notable as being the time in which [[mammal]]s became very diversified and dominant. | ||
{{Cenozoic Footer}} | {{Cenozoic Footer}} | ||
| − | {{ | + | {{Paleogene Footer}} |
| + | |||
| + | ==Upper boundary: The Cretaceous-Tertiary extinction event== | ||
| + | |||
| + | The Paleogene period immediately followed the [[mass extinction]] event at the end of the [[Cretaceous]], known as the [[Mass extinction#Cretaceous-Tertiary extinction event|Cretaceous-Tertiary extinction event]] or K-T extinction event. Many forms of life perished, encompassing approximately 50 percent of all plant and animal families, the most conspicuous being the non-avian [[dinosaur]]s. The last of the pterosaurs also vanished, as well as the great sea reptiles of the Cretaceous, the mosasaurs and plesiosaurs. Mammals suffered as well, and among mollusks, the ammonites, a diverse group of coiled [[cephalopod]]s, were exterminated. As much as 57 percent of the plant species in North America may have become extinct as well. | ||
| + | |||
| + | |||
| + | Some recognize this mass extinction now as occurring at the Cretaceous-Paleogene boundary rather than the K-T boundary, because of new classification being recommended (Hinton 2006). | ||
| + | |||
| + | |||
| + | The K-T boundary that marks the separation between Cretaceous and Paleogene is visible in the geological record of much of the Earth by a discontinuity in the [[fossil]] fauna, with high [[iridium]] levels. There is also fossil evidence of abrupt changes in [[plant]]s and [[animal]]s. There is some evidence that a substantial but very short-lived climatic change may have occurred in the very early decades of the Paleocene. There are a number of theories about the cause of the K-T [[mass extinction|extinction event]], with most evidence supporting the impact of a 10 km diameter [[asteroid]] near Yucatan, [[Mexico]]. | ||
| + | |||
| + | ==Paleocene-Eocene Thermal Maximum== | ||
| + | |||
| + | The end of the Paleocene (55.5/54.8 Ma) was marked by one of the most significant periods of global change during the Cenozoic, a sudden global change, the [[Paleocene-Eocene Thermal Maximum]], which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals.The Paleogene follows the Cretaceous Period and is followed by the [[Miocene]] Epoch of the [[Neogene]] Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the rocks deposited during the 'Paleogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine subdivisions of time possible in the relatively recent geologic past, when more information is preserved. By dividing the [[Tertiary]] Period into two periods instead of five epochs, the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic Eras. | ||
| + | |||
| + | |||
| + | |||
| + | [[Image:65 Myr Climate Change.png|thumb|300px|right|Climate change during the last 65 million years. The Paleocene-Eocene Thermal Maximum is labeled PETM and is likely to be understated by a factor of 2 or more due to coarse sampling and averaging in this data set.]] | ||
| + | The end of the Paleocene (55.5/54.8 mya) was marked by one of the most significant periods of global change during the Cenozoic, the ''Paleocene-Eocene Thermal Maximum''. In an event marking the start of the [[Eocene]], the planet heated up in one of the most rapid and extreme global warming events recorded in geologic history, currently either the Paleocene-Eocene Thermal Maximum or the ''Initial Eocene Thermal Maximum'' (PETM or IETM). Sea surface temperatures rose between 5 and 8°C over a period of a few thousand years, but in the high Arctic, sea surface temperatures rose to a sub-tropical ~23°C/73°F. This upset oceanic and atmospheric circulation and led to the [[extinction]] of numerous deep-sea benthic foraminifera and on land, a major turnover in [[mammal]]s. | ||
| + | |||
| + | |||
| + | |||
| + | ==Paleogene biota== | ||
| + | Lasting 42 million years, the Paleogene period is most notable as being the time in which [[mammal]]s [[evolution|evolved]] from small, simple forms into diverse [[animal]]s in the wake of the [[mass extinction]] that ended the preceding [[Cretaceous]] Period. | ||
| + | Some of these mammals would evolve into large forms that would dominate the land, while others would become capable of living in [[ocean|marine]], specialized terrestrial and even airborne environments. [[Bird]]s also evolved considerably during this period changing into roughly-modern forms. Most other branches of [[life]] on [[earth]] remained relatively unchanged in comparison to birds and mammals during this time period. Some [[plate tectonics|continental motion]] took place. [[Climate]]s cooled somewhat over the duration of the Paleogene and inland seas retreated from North America early in the Period. | ||
| + | |||
| + | |||
| + | |||
{{credit|93112833}} | {{credit|93112833}} | ||
[[Category:Life sciences]] | [[Category:Life sciences]] | ||
Revision as of 17:59, 11 December 2006
The Paleogene (alternatively Palaeogene) period is a major division of the geologic time scale and the first of two periods that mark our current era, the Cenozoic. The Paleogene began 65.5 ± 0.3 million years ago (mya) and ended 23.03 ± 0.05 mya. The Paleogene begins at the end of the Cretaceous period and is followed by the Neogene period, the current and final period of the Cenozoic. The Paleogene encompasses the Paleocene, Eocene, and Oligocene epochs.
The Tertiary was one prominent as the period that began at the end of the Cretaceous period. 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. When the term Tertiary is used now, it is generally as a "sub-era," which includes the Paleogene and part of the Neogene, rather than a "period" of geologic time (Hinton 2006). The Quaternary likewise has been subsumed into the Neogene and considered a "sub-era," although this remains quite controversial; the change has been opposed by many geologists, botanists, zoologists, and others (Hinton 2006).
The end of the Cretaceous period and the beginning of the Paleogene (originally Tertiary) 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, including most dinosaurs. Some recognize this mass extinction now as occurring at the Cretaceous-Paleogene boundary rather than the K-T boundary (Hinton 2006).
Another major phenomena during the Paleogene was one of the most significant periods of global change during the Cenozoic, the Paleocene-Eocene Thermal Maximum.
Lasting 42 million years, the Paleogene period is most notable as being the time in which mammals became very diversified and dominant.
| Cenozoic era (65-0 mya) | |
|---|---|
| Paleogene | Neogene Quaternary |
| Paleogene period | ||
|---|---|---|
| Paleocene epoch | Eocene epoch | Oligocene epoch |
| Danian | Selandian Thanetian |
Ypresian | Lutetian Bartonian | Priabonian |
Rupelian | Chattian |
Upper boundary: The Cretaceous-Tertiary extinction event
The Paleogene period immediately followed the mass extinction event at the end of the Cretaceous, known as the Cretaceous-Tertiary extinction event or K-T extinction event. Many forms of life perished, encompassing approximately 50 percent of all plant and animal families, the most conspicuous being the non-avian dinosaurs. The last of the pterosaurs also vanished, as well as the great sea reptiles of the Cretaceous, the mosasaurs and plesiosaurs. Mammals suffered as well, and among mollusks, the ammonites, a diverse group of coiled cephalopods, were exterminated. As much as 57 percent of the plant species in North America may have become extinct as well.
Some recognize this mass extinction now as occurring at the Cretaceous-Paleogene boundary rather than the K-T boundary, because of new classification being recommended (Hinton 2006).
The K-T boundary that marks the separation between Cretaceous and Paleogene is visible in the geological record of much of the Earth by a discontinuity in the fossil fauna, with high iridium levels. There is also fossil evidence of abrupt changes in plants and animals. There is some evidence that a substantial but very short-lived climatic change may have occurred in the very early decades of the Paleocene. There are a number of theories about the cause of the K-T extinction event, with most evidence supporting the impact of a 10 km diameter asteroid near Yucatan, Mexico.
Paleocene-Eocene Thermal Maximum
The end of the Paleocene (55.5/54.8 Ma) was marked by one of the most significant periods of global change during the Cenozoic, a sudden global change, the Paleocene-Eocene Thermal Maximum, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals.The Paleogene follows the Cretaceous Period and is followed by the Miocene Epoch of the Neogene Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the rocks deposited during the 'Paleogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine subdivisions of time possible in the relatively recent geologic past, when more information is preserved. By dividing the Tertiary Period into two periods instead of five epochs, the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic Eras.
The end of the Paleocene (55.5/54.8 mya) was marked by one of the most significant periods of global change during the Cenozoic, the Paleocene-Eocene Thermal Maximum. In an event marking the start of the Eocene, the planet heated up in one of the most rapid and extreme global warming events recorded in geologic history, currently either the Paleocene-Eocene Thermal Maximum or the Initial Eocene Thermal Maximum (PETM or IETM). Sea surface temperatures rose between 5 and 8°C over a period of a few thousand years, but in the high Arctic, sea surface temperatures rose to a sub-tropical ~23°C/73°F. This upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals.
Paleogene biota
Lasting 42 million years, the Paleogene period is most notable as being the time in which mammals evolved from small, simple forms into diverse animals in the wake of the mass extinction that ended the preceding Cretaceous Period. Some of these mammals would evolve into large forms that would dominate the land, while others would become capable of living in marine, specialized terrestrial and even airborne environments. Birds also evolved considerably during this period changing into roughly-modern forms. Most other branches of life on earth remained relatively unchanged in comparison to birds and mammals during this time period. Some continental motion took place. Climates cooled somewhat over the duration of the Paleogene and inland seas retreated from North America early in the Period.
Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
The history of this article since it was imported to New World Encyclopedia:
Note: Some restrictions may apply to use of individual images which are separately licensed.
