Ordovician
From Tardis Wiki, the free Doctor Who reference
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)"])
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