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The Neogene is a geologic period and system in the International Commission on Stratigraphy (ICS) Geologic Timescale starting 23.03 million years ago and ending 2.58 million years ago. The second period in the Cenozoic Era, it follows the Paleogene Period and is succeeded by the Quaternary Period. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. The Neogene officially covers about 20 million years, making it the shortest period of the Phanerozoic Eon; however 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. 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''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Neogene」の詳細全文を読む スポンサード リンク
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