The deep sea is nature’s motherboard, according to author and aquatic explorer Susan Casey. It absorbs heat, buffers excess carbon, drives our climate and regulates the earth’s geochemistry. It’s also home to mountains taller than the Swiss Alps and populated by a cast of “marvelous weirdos:” creatures that have two mouths or three hearts, or transparent heads or eyes in the middle of their backs. And it’s almost completely unknown to us: 80% of the sea floor has never been mapped in any detail. Casey joins us to talk about some of the wonders of the deep sea – and the ecological threats it faces. Her book is “The Underworld: Journeys to the Depths of the Ocean.”

Guests:Susan Casey, author, "The Underworld: Journeys to the Depths of the Ocean." Her previous books include “The Wave: In Pursuit of the Rogues, Freaks, and Giants of the Ocean,” and “The Devil’s Teeth: A True Story of Obsession and Survival Among America’s Great White Sharks.”