On any night in early June, if you stand on the right beaches of America's East Coast, you can travel back in time all the way to the Jurassic. For as you watch, thousands of horseshoe crabs will emerge from the foam and scuttle up the beach to their...

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 met...