Ocean explorer Robert Ballard takes us on a mindbending trip to hidden worlds underwater, where he and other researchers are finding unexpected life, resources, even new mountains. He makes a case for serious exploration and mapping. Google Ocean, anyone?

Among the most accomplished and well known of the world's deep-sea explorers, Dr. Robert Ballard is best known for his historic discoveries of hydrothermal vents, the sunken R.M.S. Titanic, the German battleship Bismarck, and numerous other contemporary and ancient shipwrecks around the world. During his long career he has conducted more than 15...