What lies beyond the reach of the naked eye, and how do these hidden forces shape our lives? This hour, TED speakers reveal forgotten cities, underwater canyons, tiny parasites, and a boiling river. TED speakers include computer scientist Abe Davis, ocean explorer Robert Ballard, science writer Ed Yong, space archaeologist Sarah Parcak, and geoscientist Andrés Ruzo. (Original broadcast date: March 18, 2016)