奥陶纪 [地质] Ordovician ; [地质] Ordovician period ; cambro-ordovician ; Ordovices
奥陶纪的 ordovician
寒武-奥陶纪 Cambro-ordovician ; cambrian-ordovician
晚奥陶纪 Late Ordovician ; taconic
下奥陶纪 lower ordovician
奥陶纪前 Pre-Ordovician ; pre ordovician
奥陶纪碳酸盐岩 The Ordovician carbonate rocks
奥陶纪灰岩 O limestone
奥陶纪地层 Ordovician stratigraphy
即奥陶纪末的塔康运动 Toconic Orogeny
美国西部干燥的山脉包含了距今4.4亿至5.1亿年前的奥陶纪岩石，其中充斥着热带海洋生物生存的迹象。
The dry mountain ranges of the western United States contain rocks dating back 440 to 510 million years, to the Ordovician period, and teeming with evidence of tropical marine life.
在奥陶纪，大多数生命都生活在海洋里，所以海洋生物，例如三叶虫、腕足类动物与笔石动物的数量在此时急剧减少。
During the Ordovician, most life was in the sea, so it was sea creatures such as trilobites, brachiopods and graptolites that were drastically reduced in number.
其它四次大灭绝对生物进化产生了巨大的影响，动物因此逐渐处于优势地位，但是，奥陶纪末期大灭绝发生前后，处于支配地位的动物物种没有发生变化。
Although the four other Big Five extinction events led to huge changes in which animals rose to prominence, the same animals that dominated before the end-Ordovician dominated afterward.
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