Oklahoma: A Story Through Her People

Scientists date the sedimentary rocks formed by ancient seas that once covered
Oklahoma at more than one billion years old. The up thrusts that formed the state’s
mountain systems—and corresponding sinking that allowed shallow seas to leave
deposits of mud and swamp plants—resulted in expansive deposits of petroleum,
shale, limestone, and coal, an important part of the state’s modern economy.
Fossilized remains of snails, trilobites, and other sea creatures, along with preserved
coral reefs, prove the existence of the ancient seas.
The first amniotes, resembling small lizards, evolved from their amphibious ancestors roughly 300 million years ago— in order to adapt to drier environments as the seas receded.
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