On the cover of Claire Nivola’s picture-book biography of Sylvia Earle, a small figure in a wet suit swims with a large school of fish in an expanse of blue. As the book goes on to make clear, this pioneering oceanographer has long been immersed in her work. Even as a child, Earle felt at home in nature, scrutinizing the flora and fauna on her country farm. When she moved to the Gulf Coast at the age of 12, the ocean world opened up for her. With wonderful details and color, the book follows her quest, starting with just a pair of goggles, to explore more and more of the sea.

One highlight involves spending two weeks in a deep-sea laboratory, swimming among ocean creatures for up to 12 hours a day. Nivola’s illustrations of this experience, one rendered in a gorgeous deep indigo and the other bright with daylight, reveal the variety of living beings tucked in and around coral reefs.

The book’s text is likewise sharp and vivid, full of Earle’s musings: “Whales are like swallows . . . like otters. . . . They move in any direction.” After celebrating the mystery and vastness of the world’s oceans — only 5 percent has been explored — Nivola offers a sobering afterword about the damage humans do to this precious resource.

Frances Foster/Farrar Straus Giroux. Ages 4-8