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 spawning grounds, as they've done, nearly unchanged, for more than 440 million years. Horseshoe crabs are far from the only contemporary manifestation of Earth's distant past, and in Relics , world-renowned...