The Underworld: Journeys to the Depths of the Ocean zips as enthrallingly along as the state-of-the-art submersibles in which journalist Susan Casey deep-sea dives. The 2014 disappearance of Malaysia Airlines Flight 370 over the Indian Ocean ignited Casey’s curiosity about what lay deeper within the marine worlds she had previously covered in her bestselling The Wave, The Devil’s Teeth and Voices in the Ocean. As Casey writes, the ensuing high-tech search for the plane using robots and sonar revealed a “symphony of extremes, a playlist of geology’s greatest hits,” including mountainous volcanoes, deep crevasses, towering cliffs and “a riot of unique species” never seen before. The Underworld is her dazzling answer to the age-old, tantalizing question about the ocean’s abyss: “What’s down there?”
Casey provides a thorough historical run-up of how the deep ocean has intrigued cartographers and explorers for centuries. From Olaus Magnus’ 1539 illustrated map, the Carta Marina, which inspired the popular belief that monsters filled the deep, to today’s OceanX, a nonprofit initiative whose mission is “to explore the ocean and bring it back to the world,” Casey colorfully explains how far our understanding of the ocean has come. Yet as humans we tend to look up, not down. Space continues to hold our attention. This, Casey argues, shortchanges the great lifesaving potential of the ocean, where even tiny microbes have the power to transform and save our planet.
The Underworld begins in January 2021, with Casey equally thrilled and terrified as she prepares to take her first dive in a submersible. Starting from the epipelagic (or sunlight) zone, she will drop through several regions to reach the hadal zone—fittingly named after Hades, Greek god of the underworld—which starts at 20,000 feet and extends beneath the seafloor into trenches and troughs. It is a wild ride as she describes the sea’s inhabitants flitting past the viewport: supergiant squids and transparent creatures with glass skeletons, three hearts, eight legs or “eyes that could swivel in any direction.” In the hadal zone, a submersible faces 16,000 pounds of pressure per square inch, and any mechanical flaw is likely to be fatal.
But that is not the danger Casey worries about. Rather, she worries about the imminent threat of deep-sea mining, poised to wreak havoc on the ocean’s floor, destroy sea life and alter the ocean’s ecosystem forever. Casey warns that the global efforts of environmental activists to stop the cataclysmic mining could ultimately fall short, and The Underworld compels readers to pay attention and learn more about this mysterious but vital world.