Cenozoic era

One of the major divisions of geological time, the most recent geological period following the Mesozoic Era. It refers to the period from about 66 million years ago to the present. The strata formed during the Cenozoic Era are called the Cenozoic. The Cenozoic Era is divided into three periods: the Paleogene, Neogene, and Quaternary. The Paleogene is further divided into the Paleocene, Eocene, and Oligocene, the Neogene into the Miocene and Pliocene, and the Quaternary into the Pleistocene and Holocene. Unofficially, the Paleogene and Neogene are collectively referred to as the Tertiary in Japan. The Cenozoic Era is also referred to as the age of mammals, and after the extinction of the large dinosaurs at the end of the Mesozoic Era, the evolution and development of a wide variety of mammals, representative of land creatures, was remarkable. It is also characterized by the evolution and development of all organisms other than mammals that can be seen today. In large mountain ranges such as the Himalayas and the Alps, the current topography was formed through a series of mountain-building movements, including folding and uplift. The Quaternary Period is only 2.58 million years shorter than the Tertiary Period, but is characterized by the emergence and development of humans and ice ages. The climate of the Cenozoic Period was warm until the middle of the Miocene Period of the Neogene Period, and then cooled. The latter half of the Quaternary Period was a period of drastic climate change, as symbolized by repeated glacial and interglacial periods. We are currently in a warm interglacial period, which has continued for about 10,000 years since the last glacial period of the Quaternary Period. This period is called the Holocene, and the previous Quaternary Period is called the Pleistocene. Planktonic microfossil biostratigraphy, paleomagnetic stratigraphy, and radioisotope chronology have made it possible to accurately compare distant regions, and the detailed chronology of the Cenozoic Period is becoming clear.

[Toshiyuki Yamaguchi August 19, 2015]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

地質時代の大区分の一つで、中生代に続くもっとも新しい地質時代。およそ6600万年前から現在までの時代をいう。新生代に形成された地層を新生界という。新生代は古第三紀、新第三紀および第四紀に三分される。古第三紀は古いほうから暁新世(ぎょうしんせい)、始新世、漸新世に、新第三紀は中新世、鮮新世に、第四紀は更新世、完新世に細分される。非公式ではあるが、日本では古第三紀と新第三紀は第三紀と総称される。新生代は哺乳類(ほにゅうるい)の時代とも表現されるように、中生代末の大形の恐竜の絶滅後、陸上を代表する多種多様な哺乳類の進化発展が著しい。また哺乳類以外の生物でも、現在みられるあらゆる生物群の進化発展で特徴づけられる。ヒマラヤ―アルプスなどの大山脈では褶曲(しゅうきょく)、隆起運動の一連の造山運動を経て、現在みられる地形が形成された。第四紀は第三紀に比べておよそ258万年という短い時間しか経ていないが、人類の出現、発展および氷河時代などで特徴づけられる。新生代の気候は、新第三紀中新世中期までは温暖で、以降寒冷化し、とくに第四紀後半は氷期・間氷期の繰り返しで象徴されるように気候変化の激しい時代であった。現在は温暖な間氷期にあたり、それは第四紀の最後の氷期以来約1万年継続している。この時期を完新世、その前の第四紀を更新世とよんでいる。浮遊性微化石による生層序、古地磁気層序、また、放射性同位体による年代層序などによって遠隔地間の正確な対比が可能となり、新生代の詳しい編年が明らかになりつつある。

［山口寿之　2015年8月19日］

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