TheNeogene (/ˈniː.ədʒiːn/NEE-ə-jeen,[6][7]) is ageologic period and system that spans 20.45 million years from the end of thePaleogene Period 23.04 Ma (million years ago) to the beginning of the presentQuaternary Period 2.58 Ma. It is the second period of theCenozoic and the eleventh period of thePhanerozoic. The Neogene is sub-divided into twoepochs, the earlierMiocene and the laterPliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, theQuaternary.[8] The term "Neogene" was coined in 1853 by the Austrian palaeontologistMoritz Hörnes (1815–1868).[9] The earlier termTertiary Period was used to define the span of time now covered by Paleogene and Neogene and, despite no longer being recognized as a formalstratigraphic term, "Tertiary" still sometimes remains in informal use.[10]
During this period,mammals andbirds continued to evolve into modern forms, while other groups of life remained relatively unchanged. The first humans (Homo habilis) appeared in Africa near the end of the period.[11] Some continental movements took place, the most significant event being the connection ofNorth andSouth America at theIsthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific to the Atlantic Ocean, leaving only theGulf Stream to transfer heat to theArctic Ocean. The global climate cooled considerably throughout the Neogene, culminating in a series of continentalglaciations in theQuaternary Period that followed.
The global climate became more seasonal and continued an overall drying and cooling trend which began during thePaleogene. TheEarly Miocene was relatively cool;[12] Early Miocene mid-latitude seawater and continental thermal gradients were already very similar to those of the present.[13] During theMiddle Miocene, Earth entered a warm phase known as the Middle Miocene Climatic Optimum (MMCO),[12] which was driven by the emplacement of theColumbia River Basalt Group.[14] Around 11 Ma, the Middle Miocene Warm Interval gave way to the much cooler Late Miocene.[12] The ice caps on both poles began to grow and thicken, a process enhanced by positive feedbacks from increased formation of sea ice.[15] Between 7 and 5.3 Ma, a decrease in global temperatures termed the Late Miocene Cooling (LMC) ensued, driven by decreases in carbon dioxide concentrations.[16] During the Pliocene, from about 5.3 to 2.7 Ma, another warm interval occurred, being known as the Pliocene Warm Interval (PWI), interrupting the longer-term cooling trend. ThePliocene Thermal Maximum (PTM) occurred between 3.3 and 3.0 Ma.[12] During the Pliocene,Green Sahara phases of wet conditions inNorth Africa were frequent and occurred about every 21 kyr, being especially intense when Earth's orbit's eccentricity was high.[17] The PWI had similar levels of atmospheric carbon dioxide to contemporary times and is often seen as an analogous climate to the projected climate of the near future as a result ofanthropogenic global warming.[18] Towards the end of the Pliocene, decreased heat transport towards the Antarctic resulting from a weakening of theIndonesian Throughflow (ITF) cooled the Earth, a process that exacerbated itself in a positive feedback as sea levels dropped and the ITF diminished and further limited the heat transported southward by theLeeuwin Current.[19] By the end of the period the first of a series of glaciations of thecurrent Ice Age began.[20]
Marine and continental flora and fauna have a modern appearance. The reptile groupChoristodera went extinct in the early part of the period, while the amphibians known asAllocaudata disappeared at the end of it. Neogene also marked the end of the reptilian generaLangstonia andBarinasuchus, terrestrial predators that were the last surviving members ofSebecosuchia, a group related to crocodiles. The oceans were dominated by large carnivores likemegalodons andlivyatans, and 19 million years ago about 70% of all pelagic shark species disappeared.[21]Mammals andbirds continued to be the dominant terrestrial vertebrates, and took many forms as they adapted to various habitats.Ungulates in North America became noticeably morecursorial and increased their stride lengths across the Oligocene-Miocene boundary, likely in response to the increased habitat openness during the Miocene.[22] An explosive radiation of ursids took place at the Miocene-Pliocene boundary.[23] The firsthominins, the ancestors of humans, appeared near the end of the period.[11][24]
About 20 Magymnosperms in the form of someconifer andcycad groups started to diversify and produce more species due to the changing conditions.[25] In response to the cooler, seasonal climate, tropical plant species gave way todeciduous ones and grasslands replaced many forests. Grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such ashorses,antelope, andbison. Ice age mammals like themammoths andwoolly rhinoceros were common inPliocene. With lower levels of CO2 in the atmosphere,C4 plants expanded and reached ecological dominance in grasslands during the last 10 million years. AlsoAsteraceae (daisies) went through a significantadaptive radiation.[26]Eucalyptus fossil leaves occur in theMiocene of New Zealand, where the genus is not native today, but have been introduced from Australia.[27]
The Neogene traditionally ended at the end of the Pliocene Epoch, just before the older definition of the beginning of theQuaternary Period; many time scales show this division.
However, there was a movement amongst geologists (particularlymarine 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.[8] By dividing theCenozoic 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.
TheInternational 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 theGelasian Stage. In the 2004 proposal of the ICS, the Neogene would have consisted of theMiocene andPliocene Epochs.[28] TheInternational 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 theGauss-Matuyama magnetostratigraphic boundary.[29][30] In 2006 ICS and INQUA reached a compromise that made Quaternary a sub-era, subdividing Cenozoic into the old classicalTertiary and Quaternary, a compromise that was rejected byInternational Union of Geological Sciences because it split both Neogene and Pliocene in two.[31]
Following formal discussions at the 2008 International Geological Congress in Oslo, Norway,[32] the ICS decided in May 2009 to make the Quaternary the youngest period of the Cenozoic Era with its base at 2.58 Ma and including the Gelasian Age, which was formerly considered part of the Neogene Period and Pliocene Epoch.[33] Thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Ma.
^abTucker, M.E. (2001).Sedimentary petrology: an introduction to the origin of sedimentary rocks (3rd ed.). Osney Nead, Oxford, UK: Blackwell Science.ISBN978-0-632-05735-1.
^Hörnes, M. (1853)."Mittheilungen an Professor Bronn gerichtet" [Reports addressed to Professor Bronn].Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde (in German):806–810.hdl:2027/hvd.32044106271273.From p. 806:"Das häufige Vorkommen der Wiener Mollusken … im trennenden Gegensatze zu den eocänen zusammenzufassen." (The frequent occurrence of Viennese mollusks in typical Miocene as well as in typical Pliocene deposits motivated me – in order to avoid the perpetual monotony [of providing] details about the deposits – to subsume both deposits provisionally under the name "Neogene" (νεος new and γιγνομαι to arise) in distinguishing contrast to the Eocene.)
^abSpoor, Fred; Gunz, Philipp; Neubauer, Simon; Stelzer, Stefanie; Scott, Nadia; Kwekason, Amandus; Dean, M. Christopher (March 2015). "Reconstructed Homo habilis type OH 7 suggests deep-rooted species diversity in early Homo".Nature.519 (7541):83–86.Bibcode:2015Natur.519...83S.doi:10.1038/nature14224.PMID25739632.S2CID4470282.
.png)
.jpg)
