Early in her time at the Bureau of Fisheries, Carson drafted an eleven-page essay about sea life called “The World of Waters.” The head of her department told her that it was too good for a government brochure and suggested that she send it to The Atlantic. After it was published, as “Undersea,” Carson began writing her first book under the largesse of F.D.R.’s New Deal, in the sense that she drafted it on the back of National Recovery Administration stationery, while working for what became, in 1939, the U.S. Fish and Wildlife Service. “Under the Sea-Wind” appeared a few weeks before the Japanese bombed Pearl Harbor, and sank like a battleship.

Carson, who spent the meat-rationed war instructing housewives in how to cook little-known fish, grew restless. She pitched a piece to the Reader’s Digest about DDT. During the war, chemical companies had sold the pesticide to the military to stop the spread of typhus by killing lice. After the war, they began selling DDT and other pesticides commercially, to be applied to farms and gardens. Carson, reading government reports on fish and wildlife, became alarmed: DDT hadn’t been tested for civilian use, and many creatures other than insects appeared to be dying. She proposed an article on the pesticide, investigating “whether it may upset the whole delicate balance of nature if unwisely used.” The Reader’s Digest was not interested.

Writing at night, Carson began another book, hoping to bring to readers the findings of a revolution in marine biology and deep-sea exploration by offering an ecology of the ocean. “Unmarked and trackless though it may seem to us, the surface of the ocean is divided into definite zones,” she explained. “Fishes and plankton, whales and squids, birds and sea turtles, are all linked by unbreakable ties to certain kinds of water.” But the state of research also meant that mysteries abided: “Whales suddenly appear off the slopes of the coastal banks where the swarms of shrimplike krill are spawning, the whales having come from no one knows where, by no one knows what route.”

Carson had taken on a subject and a field of research so wide-ranging that she began calling the book “Out of My Depth,” or “Carson at Sea.” She was haunted, too, by a sense of foreboding. In 1946, she’d had a cyst in her left breast removed. In 1950, her doctor found another cyst. After more surgery, she went to the seashore, Nags Head, North Carolina. “Saw tracks of a shore bird probably a sanderling, and followed them a little, then they turned toward the water and were soon obliterated by the sea,” she wrote in field notes that she kept in spiral-bound notebooks. “How much it washes away, and makes as though it had never been.”

When Carson finished the book, The Atlantic declined to publish an excerpt, deeming it too poetic. William Shawn, the editor of The New Yorker, did not share this reservation. “The Sea Around Us” appeared in these pages, in 1951, as a three-part Profile of the Sea, the magazine’s first-ever profile of something other than a person. Letters from readers poured in—“I started reading with an o-dear-now-whats-this attitude, and found myself entranced,” one wrote—and many declared it the most memorable thing ever published in the magazine and, aside from John Hersey’s “Hiroshima,” the best.

“The Sea Around Us” won the National Book Award, and remained on the New York Times best-seller list for a record-breaking eighty-six weeks. Reissued, “Under the Sea-Wind” became a best-seller, too. “Who is the author?” readers wanted to know. Carson’s forcefully written work drew the supposition from male reviewers that its female author must be half-man. A reporter for the Boston Globe wrote, “Would you imagine a woman who has written about the seven seas and their wonders to be a hearty physical type? Not Miss Carson. She is small and slender, with chestnut hair and eyes whose color has something of both the green and blue of sea water. She is trim and feminine, wears a soft pink nail polish and uses lipstick and powder expertly, but sparingly.”

Carson shrugged that off and, resigning from her government post, began to question federal policy. When Eisenhower’s new Secretary of the Interior, a businessman from Oregon, replaced scientists in the department with political hacks, Carson wrote a letter to the Washington Post: “The ominous pattern that is clearly being revealed is the elimination from the Government of career men of long experience and high professional competence and their replacement by political appointees.”

But the greatest change wrought by Carson’s success came when, with the earnings from her biography of the ocean, she bought a tiny patch of land atop a rock in Maine, and built a small cottage there, a Walden by the sea. Carson once dived underwater, wearing an eighty-four-pound sea-diving helmet, and lasted, eight feet below, for only fifteen clouded minutes. Her real love was the shore: “I can’t think of any more exciting place to be than down in the low-tide world, when the ebb tide falls very early in the morning, and the world is full of salt smell, and the sound of water, and the softness of fog.” To fathom the depths, she read books; the walls of her house in Maine are lined with them, crammed between baskets and trays filled with sea glass and seashells and sea-smoothed stones. She wrote some of her next book, “The Edge of the Sea,” from that perch.

“My quarrel with almost all seashore books for the amateur,” she reflected, “is that they give him a lot of separate little capsules of information about a series of creatures, which are never firmly placed in their environment.” Carson’s seashore book was different, an explanation of the shore as a system, an ecosystem, a word most readers had never heard before, and one that Carson herself rarely used but instead conjured, as a wave of motion and history:

In my thoughts these shores, so different in their nature and in the inhabitants they support, are made one by the unifying touch of the sea. For the differences I sense in this particular instant of time that is mine are but the differences of a moment, determined by our place in the stream of time and in the long rhythms of the sea. Once this rocky coast beneath me was a plain of sand; then the sea rose and found a new shore line. And again in some shadowy future the surf will have ground these rocks to sand and will have returned the coast to its earlier state. And so in my mind’s eye these coastal forms merge and blend in a shifting, kaleidoscopic pattern in which there is no finality, no ultimate and fixed reality—earth becoming fluid as the sea itself.

Paul Brooks, Carson’s editor at Houghton Mifflin, once said that, as a writer, she was like “the stonemason who never lost sight of the cathedral.” She was a meticulous editor; so was he. “Spent time on the Sand chapter with a pencil between my teeth,” he wrote to her. But she didn’t like being fixed up and straightened out, warning Brooks, “I am apt to use what may appear to be a curious inversion of words or phrases”—her brine-drenched jabberwocky—“but for the most part these are peculiar to my style and I don’t want them changed.”

“The bathroom? Ah, yes, the bathroom—well, let me tell you about the bathroom.”

Writing by the edge of the sea, Rachel Carson fell in love. She met Dorothy Freeman in 1953 on the island in Maine where Carson built her cottage and where Freeman’s family had summered for years. Carson was forty-six, Freeman fifty-five. Freeman was married, with a grown son. When she and Carson weren’t together, they maintained a breathless, passionate correspondence. “Why do I keep your letters?” Carson wrote to Freeman that winter. “Why? Because I love you!” Carson kept her favorite letters under her pillow. “I love you beyond expression,” Freeman wrote to Carson. “My love is boundless as the Sea.”

Both women were concerned about what might become of their letters. In a single envelope, they often enclosed two letters, one to be read to family (Carson to her mother, Freeman to her husband), one to be read privately, and likely destined for the “Strong box”—their code for letters to be destroyed. “Did you put them in the Strong box?” Carson would ask Freeman. “If not, please do.” Later, while Carson was preparing her papers, which she’d pledged to give to Yale, Freeman read about how the papers of the writer Dorothy Thompson, recently opened, contained revelations about her relationships with women. Freeman wrote to Carson, “Dear, please, use the Strong box quickly,” warning that their letters could have “meanings to people who were looking for ideas.” (They didn’t destroy all of them: those that survive were edited by Freeman’s granddaughter and published in 1995.)

After the publication of “The Edge of the Sea” (1955), another best-seller that was also serialized in The New Yorker, Shawn wanted Carson to write a new book, to appear in the magazine, on nothing less than “the universe.” And she might have tackled it. But, when her niece Marjorie died of pneumonia, Carson adopted Marjorie’s four-year-old son, Roger, a little boy she described as “lively as seventeen crickets.” She set aside longer writing projects until, with some reluctance, she began work on a study whose title, for a long time, was “Man Against the Earth.”