The continent underwater
Coral reefs where Ohio now lies
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In the Ordovician, around 450 million years ago, North America sat on the equator and was largely covered by a shallow, warm inland sea. The Cincinnati Arch yields some of the world's best-studied Ordovician faunas, and its beds have been a reference point for evolutionary palaeoecology since the nineteenth century. The period ends in the Ordovician mass extinction, the second largest in Earth's history, tied to a short but severe glaciation while Gondwana sat over the south pole.
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Four hundred and fifty million years ago most of North America lay under a warm, shallow sea, rather like the Bahamas today. The seabed was covered in reefs built by corals and sponges. The limestone from those reefs is the same rock many American cities were later built from.
Sources
- Encyclopædia Britannica: «Ordovician Period»
- Meyer & Davis, A Sea Without Fish: Life in the Ordovician Sea of the Cincinnati Region (2009)
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