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The Ordovician was an era of Earth's history dating from 488 million to 443 million BC. It was an era of hard-shelled sea creatures such as trilobites, with no life truly living on land yet. It was bookended by two extinction events: the Cambrian-Ordovician extinction event and the Ordovician-Silurian extinction event. (PROSE: Prehistory Repeating Itself [+]Loading...["Prehistory Repeating Itself (feature)"])