As beautiful and interesting as a polished Petoskey stone specimen may be, the story of how its coral came to be preserved in Michigan’s limestone is even more compelling. It begins during the Devonian, a time period that began around 419 million years ago and lasted the next 60 million years. Known as “The Age of Fish,” the Devonian world was very different from ours, with the continents closer together and inundated by warm, shallow seas that covered much of the planet, including modern-day Michigan. And, true to its nickname, the Devonian era saw the evolution of an incredible diversity of fish and other sea life—including coral—for the first time in Earth’s history.
Earth in the Early Devonian Period
(and the approximate locations of modern-day continents)
Earth’s Geological Periods (and when they started)
