In 1901, divers found a corroded bronze mechanism in a shipwreck off Greece. When researchers finally examined it, they discovered impossible technology: an astronomical computer from 100 BCE that could predict eclipses and track planets. Then it was completely forgotten for a thousand years. If not for that shipwreck, we would never have known ancient Greeks possessed such capabilities. How much else have we forgotten? How much else never survived? The sophisticated Minoans were lost for 3,500 years. The Olmecs vanished so completely no one could explain their colossal stone heads. Sanxingdui's brilliant bronze culture left no historical trace until discovered in 1986. These civilizations existed just yesterday in geological terms—yet they faded so thoroughly that later peoples had no idea they'd been real. If entire civilizations can vanish in three thousand years, what might have vanished in three million? Drawing on a thought experiment by NASA scientist Gavin Schmidt and astrophysicist Adam Frank, Tudor Finneran explores a profound question: if an industrial civilization had existed millions of years ago, could we even detect it? The answer is unsettling. Most traces would vanish—eroded, subducted, recycled by Earth's restless geology. Finneran takes readers through deep time, examining what survives and what is lost. He shows how fragile preservation truly is, how easily knowledge disappears, and how the archaeological record is less a comprehensive history than a collection of lucky accidents. But this changes everything about how we see ourselves today. We are leaving traces—plastics, isotopes, atmospheric carbon—that will persist for millions of years. Yet within centuries, our cities will crumble. Within millennia, most evidence of our existence will be gone. We are simultaneously creating a planetary legacy and confronting our own impermanence. So how do we live meaningfully when everything we build will eventually be forgotten? Finneran weaves together archaeology, geology, and philosophy to show that impermanence is not a reason for despair but an invitation to focus on what truly matters: not monuments that last forever, but connections made, knowledge shared, and the world we leave for those who come after us. The Antikythera mechanism survived by accident. Most human achievement did not. Yet we continue to create—not because our works will last forever, but because the act of creation itself has meaning. For readers of Elizabeth Kolbert, Carl Sagan, and Alan Weisman , The Silurian Hypothesis offers a meditation on time, memory, and what it means to be human on a planet that forgets. You won't be remembered forever. So how will you live in the time you have