Neogene

Neogene Period 23.03–2.58 million years ago PreЄ Є O S D C P T J K Pg N
Mean atmospheric O 2 content over period duration	c. 21.5 vol %[1][2] (108 % of modern level)
Mean atmospheric CO 2 content over period duration	c. 280 ppm[3][4] (1 times pre-industrial level)
Mean surface temperature over period duration	c. 14 °C[5][6] (0 °C above modern level)
Key events in the Neogene view • discuss •  -24 — – -22 — – -20 — – -18 — – -16 — – -14 — – -12 — – -10 — – -8 — – -6 — – -4 — – -2 — – 0 — C e n o z o i c Paleogene N e o g e n e Quaternary M i o c e n e P l i o c e n e Aquitanian Burdigalian Langhian Serravallian Tortonian Messinian Zanclean Piacenzian         ← Messinian salinity crisis[7] ← Holocene begins 11.7 ka ago An approximate timescale of key Neogene events. Vertical axis: millions of years ago.

The Neogene (pronunciation: /ˈniːəˌdʒiːn/)^[8][9] is a geologic period and system that spans 20.4 million years from the end of the Paleogene Period 23.03 million years ago (Mya) to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary.

During this period, mammals and birds continued to evolve into roughly modern forms, while other groups of life remained relatively unchanged. Early hominids, the ancestors of humans, appeared in Africa near the end of the period. Some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific to the Atlantic ocean, leaving only the Gulf Stream to transfer heat to the Arctic Ocean. The global climate cooled considerably over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows.

Divisions

In ICS terminology, from upper (later, more recent) to lower (earlier):

The Pliocene Epoch is subdivided into 2 ages:

• Piacenzian Age, preceded by
• Zanclean Age

The Miocene Epoch is subdivided into 6 ages:

• Messinian Age, preceded by
• Tortonian Age
• Serravallian Age
• Langhian Age
• Burdigalian Age
• Aquitanian Age

In different geophysical regions of the world, other regional names are also used for the same or overlapping ages and other timeline subdivisions.

The terms Neogene System (formal) and upper Tertiary System (informal) describe the rocks deposited during the Neogene Period.

Geography

The continents in the Neogene were very close to their current positions. The Isthmus of Panama formed, connecting North and South America. The Indian subcontinent continued to collide with Asia, forming the Himalayas. Sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America.

Climate

The global climate became seasonal and continued its overall drying and cooling trend which began at the start of the Paleogene. The ice caps on both poles began to grow and thicken, and by the end of the period the first of a series of glaciations of the current Ice Age began.

Flora and fauna

Scene featuring Miocene (Early Neogene) fauna

Marine and continental flora and fauna have a modern appearance. The reptile group Choristodera became extinct in the early part of the period, while the amphibians known as Allocaudata disappeared at the end. Mammals and birds continued to be the dominant terrestrial vertebrates, and took many forms as they adapted to various habitats. The first hominids, the ancestors of humans, appeared in Africa and spread into Eurasia.

In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones and grasslands replaced many forests. Grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison.

Disagreements

The Neogene traditionally ended at the end of the Pliocene Epoch, just before the older definition of the beginning of the Quaternary Period; many time scales show this division.

However, there was a movement amongst geologists (particularly marine geologists) to also include ongoing geological time (Quaternary) in the Neogene, while others (particularly terrestrial geologists) insist the Quaternary to be a separate period of distinctly different record. The somewhat confusing terminology and disagreement amongst geologists on where to draw what hierarchical boundaries is due to the comparatively fine divisibility of time units as time approaches the present, and due to geological preservation that causes the youngest sedimentary geological record to be preserved over a much larger area and to reflect many more environments than the older geological record.^[10] By dividing the Cenozoic Era into three (arguably two) periods (Paleogene, Neogene, Quaternary) instead of seven epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras.

The International Commission on Stratigraphy (ICS) once proposed that the Quaternary be considered a sub-era (sub-erathem) of the Neogene, with a beginning date of 2.58 Ma, namely the start of the Gelasian Stage. In the 2004 proposal of the ICS, the Neogene would have consisted of the Miocene and Pliocene epochs.^[11] The International Union for Quaternary Research (INQUA) counterproposed that the Neogene and the Pliocene end at 2.58 Ma, that the Gelasian be transferred to the Pleistocene, and the Quaternary be recognized as the third period in the Cenozoic, citing key changes in Earth's climate, oceans, and biota that occurred 2.58 Ma and its correspondence to the Gauss-Matuyama magnetostratigraphic boundary.^[12] In 2006 ICS and INQUA reached a compromise that made Quaternary a subera, subdividing Cenozoic into the old classical Tertiary and Quaternary, a compromise that was rejected by International Union of Geological Sciences because it split both Neogene and Pliocene in two.^[13]

Following formal discussions at the International Geological Congress, Oslo Norway, August 2008,^[14] the ICS decided in May 2009 to make the Quaternary the youngest period of the Cenozoic Era with its base at 2.58 Mya and including the Gelasian age, which was formerly considered part of the Neogene Period and Pliocene Epoch.^[15] Thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Mya.

References

1. Image:Sauerstoffgehalt-1000mj.svg
2. Image:OxygenLevelsThroughEarthHistory.png
3. Image:Phanerozoic Carbon Dioxide.png
4. Image:CO2LevelsThroughEarthHistory.png
5. Image:All palaeotemps.png
6. Image:TemperatureLevelsOverEarthHistory.png
7. 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.
8. "Neogene". Merriam-Webster Dictionary.
9. "Neogene". Dictionary.com Unabridged. Random House.
10. Tucker, M. E. (2001) Sedimentary Petrology (3rd ed.) Blackwell Science, Osney Nead, Oxford, UK, ISBN 0-632-05735-1
11. Lourens, L., Hilgen, F., Shackleton, N.J., Laskar, J., Wilson, D., (2004) “The Neogene Period”. In: Gradstein, F., Ogg, J., Smith, A.G. (Eds.), Geologic Time Scale Cambridge University Press, Cambridge.
12. Clague, John et al. (2006) "Open Letter by INQUA Executive Committee" Quaternary Perspective, the INQUA Newsletter International Union for Quaternary Research 16(1)
13. ICS: Consolidated Annual Report for 2006, last retrieved on 15 June 2007
14. International Geological Congress, General Proceedings for 33rd congress, Oslo, August 6–14, 2008
15. See the 2009 version of the ICS geologic time scale

External links

• Digital Atlas of Neogene Life for the Southeastern United States — by San Jose State University via Web Archive.

Neogene Period
Miocene	Pliocene
Aquitanian | Burdigalian Langhian | Serravallian Tortonian | Messinian	Zanclean | Piacenzian

Preceded by Proterozoic Eon	Phanerozoic Eon
	Paleozoic Era						Mesozoic Era			Cenozoic Era
	Cambrian	Ordovician	Silurian	Devonian	Carboniferous	Permian	Triassic	Jurassic	Cretaceous	Paleogene	Neogene	4ry