• Proterozoic
Abstract from DBPedia
    The Proterozoic ( ) is a geological eon spanning the time from the appearance of oxygen in Earth's atmosphere to just before the proliferation of complex life (such as trilobites or corals) on the Earth. The name Proterozoic combines the two forms of ultimately Greek origin: protero- meaning "former, earlier", and -zoic, a suffix related to zoe "life". The Proterozoic Eon extended from 2500 mya to 541 mya (million years ago), and is the most recent part of the Precambrian "supereon." The Proterozoic is the longest eon of the Earth's geologic time scale and it is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. The well-identified events of this eon were the transition to an oxygenated atmosphere during the Paleoproterozoic; several glaciations, which produced the hypothesized Snowball Earth during the Cryogenian Period in the late Neoproterozoic Era; and the Ediacaran Period (635 to 541 Ma) which is characterized by the evolution of abundant soft-bodied multicellular organisms and provides us with the first obvious fossil evidence of life on earth.

    原生代(げんせいだい、Proterozoic)とは、地質時代の区分(累代)のひとつ。真核単細胞生物から硬い骨格を持った多細胞生物の化石が多数現れるまでの25億年前〜約5億4,100万年前を指す。元々は、先カンブリア時代以前の全ての時代を指していた。冥王代、太古代、原生代をまとめて先カンブリア時代と呼ぶこともある。太古代の次の時代で、古生代(カンブリア紀)の前の時代である。 シアノバクテリアの活動によって大気中に酸素の放出が始まり、オゾン層ができて紫外線が地表に届かなくなった。また、古細菌類から原始真核生物が分岐し、さらにαプロテオバクテリア(後のミトコンドリア)が共生することで現在の真核生物が成立した。後期には多細胞生物も出現した。