When the American republic was founded, the Earth was no more than 75,000 years old. No contemporary thinker imagined it could possibly be older. Thus Thomas Jefferson was confident that woolly mammoths must still live in “the northern and western parts of America,” places that “still remain in their aboriginal state, unexplored and undisturbed by us.” The idea that mammoths or any other kind of creature might have ceased to exist was, to him, inconceivable. “Such is the œconomy of nature,” he