We know the ocean is full of creatures that can make their own light, a reef that houses 25 percent of all known ocean species, and about 20 million pounds of gold. We've begun to explore the deepest-known trench of the ocean--7 miles below the water's surface--and travel along underwater mountain ranges that are almost long enough to stretch around the world twice. What we have found has been incredible, despite having explored less than 20 percent...