“The most interesting section at John Boyd Thacher State Park are the layers in the cliff face that date to the Silurian and Devonian periods,” the National Park Service says, which are collectively referred to as the Middle Paleozoic Era, from 444 to 359 million years ago, a time in the Earth’s history characterized by high sea levels with expansion of marine invertebrates, reef communities, and fish. “This era also marks the emergence of plants and insects on land, and near the end of the Devonian Period, the appearance of four-legged animals.”