Quick: How many nuclear warheads were detonated above-ground by 1963?

If your answer was something just north of two, I wouldn’t blame you. I wasn’t yet born then myself, and the idea of nuclear bombs exploding above Nevada is hard to fathom. The answer, I learned in the opening chapter of William Souder’s new biography of Rachel Carson, is more than 500. The United States was responsible for about 200 of those.

The story of Carson’s life is the story of an era that is quite recent but also strangely distant from our own, in which the twin threats of nuclear fallout and chemical use were the subject of national debate. Souder makes this plain in the opening scene, with a reporter asking President Kennedy about growing concern over the use of the pesticide DDT. He responded that his administration was looking into it, “particularly, of course, since Miss Carson’s book.”

The scene highlights an equally remarkable aspect of the times in which Carson lived. A woman could write a book about the dangers posed by a new generation of pesticides, and that book — made popular in part because of a three-part serialization in the New Yorker before publication — would be so widely read and debated that the president didn’t even have to mention its title, Silent Spring. Everyone was talking about Miss Carson’s book. It is hard to envision, in today’s crowded media landscape, any book capturing the nation’s attention in the same way.

This is the great strength of On a Farther Shore. Without overstating the point, Souder draws a portrait of cultural and political life in the middle of the 20th century and places Carson squarely at the center of it. Imagine: In 1951, a little-known field biologist publishes a poetic and immaculately researched account of oceans and the life they contain, employing a narrative that begins more than 2 billion years ago, encompasses the birth of the moon, and proceeds straight through to modern times, and The Sea Around Us rises to the top of the bestseller list and sits there for 39 weeks.

It was a different time for science and a different time for science writers. Today’s writers might cheer as they read about Carson coolly declining her publisher’s requests that she give interviews and attend book signings: Such distractions would be shortsighted, “as her work could go forward only if she could maintain her life as it had been before The Sea Around Us.

Souder makes it clear that Carson had enough distractions as it was. She’d worked as a government biologist and writer from 1936 until 1952, when sales of her book allowed her to quit her job and write full-time. She bought a plot of land near Boothbay Harbor, Maine, and had a summer cottage built on it. There she met her neighbors, Stan and Dorothy Freeman, and began a romantic relationship with Mrs. Freeman that lasted the rest of Carson’s life.

The women’s letters were unambiguously passionate: In 1954, Carson wrote to Freeman, “But oh darling, I want to be with you so terribly that it hurts!” While her husband napped, Freeman wrote a letter from another bedroom in her house, telling Carson that she was writing from “the corner that belongs in my heart only to you — you know where and why.” One Christmas they shared a hotel room in New York, and the letters leading up to that rendezvous were concerned with whether Carson should register under an alias and whether the women would be able to “restrain themselves long enough to get up to their room,” to use Souder’s paraphrasing. In spite of the heated language, Souder suggests that sex “seems not to have been part of their relationship, or at least not an essential feature of it,” and that their feelings for each other “existed in a realm above ordinary physical love and desire.”