On dry land, most organisms are confined to the surface, or at most to altitudes of a hundred meters--the height of the tallest trees. In the oceans, though, living space has both vertical and horizontal dimensions: with an average depth of 3800 meters, the oceans offer 99% of the space on Earth where life can develop. And the deep sea, which has been immersed in total darkness since the dawn of time, occupies 85% of ocean space, forming the planet's...