Oceanographer Sylvia Earle was the first person to walk solo on the bottom of the sea, under a quarter mile of water. She has watched humanity’s enduring fascination with “outer space” while she has delighted in “inner space” — the alien and increasingly endangered worlds beneath earth’s waters. These frontiers, as Sylvia Earle points out, are our very life-support system. She takes us inside the knowledge she’s gathered from a lifetime of research and literally swimming with sharks. This interview is edited and produced with music and other features in the On Being episode “Sylvia Earle — Her Deepness.” Find more at onbeing.org.