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The Cambrian–Ordovician extinction event occurred approximately 488 million years ago (m.y.a.). This early Phanerozoic Eon extinction event eliminated many brachiopods and conodonts, and severely reduced the number of trilobite species. It was preceded by the less-documented (but probably worse) End Botomian extinction event around 517 million years ago and the Dresbachian event about 502 million years ago. The Cambrian–Ordovician event ended the Cambrian Period, and led into the Ordovician Period in the Paleozoic Era. ==Theories== * Glaciation * Depletion of oxygen in marine waters * Flood basalt event (Kalkarindji large igneous province, Australia) 〔Kravchinsky, V. A. (2012). Paleozoic large igneous provinces of Northern Eurasia: Correlation with mass extinction events. Global and Planetary Change, 86, 31-36.〕 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「Cambrian–Ordovician extinction event」の詳細全文を読む スポンサード リンク
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