Oceanographer Sylvia Earle, affectionately by her fellow scientists as “Her Deepness,” 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.