Humans have done a pretty good job of exploring the earth thus far - climbing mountains, crossing continents, and placing our flags all over the place in the name of science. But one part of the world that has remained pretty mysterious to us also happens to cover more than 70 percent of its surface: the ocean. True, we have sailed across it plenty of times, drill for oil in it, and managed to create reality shows about fishing in it. Yet we still have to learn a lot about it - from glowing oceans to massive deep-sea creatures and underwater eco-systems with thousands of undiscovered, basically alien species. Probably more than any place on earth, the ocean is full of fascinating stuff that we just don't know about - not yet. This video by SciShow presents seven of these mysterious ocean topics.