A geological saga that digs deep, revealing how even the most ordinary rocks can be stepping stones to the hidden history of our planet. Unearthing the Underworld reveals the hidden world of rocks—the keepers of secrets of past environments, changing climates, and the pulse of life over billions of years. Even the most seemingly ordinary stone can tell us much about the history of this planet, opening vistas of ancient worlds of ice, raging floods, strange unbreathable atmospheres, and prehistoric worlds teeming with life. Remarkably, many types of rocks owe their existence to living organisms—from the remains of bodies of dead animals to rocks formed from rotting ancient forests, or even created by the activity of fungi, bacteria, and viruses. Anything but dull and uninteresting, rocks are intriguing portals that illuminate the secret underworld upon which we live.