“Rachel Carson: Witness for Nature” by Linda Lear is the biography that finally does justice to the life of one of this country’s most extraordinary women.

Rachel Carson is widely acknowledged as the scientist-writer who launched the modern environmental movement with the publication of “Silent Spring” in 1962. During the past 35 years, “Silent Spring,” which exposed the indiscriminate use of the pesticide DDT, emerged as one of the most influential books of this century.

Until this week, however, the woman who wrote this book remained the subject of junior biographies and less-than-complete portrayals. “The House of Life,” the biographical reader written by Paul Brooks, her editor at Houghton Mifflin, provided the broad outlines of her life as a writer, but biographical details and research were cursory at best.

Carson’s published correspondence with her closest friend later in life, Dorothy Freeman (mother of University of Maine Professor Stanley Freeman Jr.), titled “Always Rachel” and edited by Dorothy’s granddaughter, Martha Freeman, provides an in-depth look into a singularly important relationship during the last 12 years of Carson’s life. As valuable as this treasure trove is, it is not a portrait of the whole person or her entire life, nor could it be.

Lear’s biography falls seven pages short of 500 pages, with an additional 100 pages of notes. It’s a thorough, unsentimental, well-written treatment of Carson’s entire life, from her childhood in the working-class town of Springdale near Pittsburgh to the scattering of a portion of her ashes off Cape Newagen, Southport Island, Maine.

Carson’s writing career began at age 10 when she contributed an article to the children’s section of St. Nicholas Magazine and ended with letters dictated to friends when she was critically ill after cancer surgery. The published major works of her adult life began with lyrical, scientifically accurate descriptions of the sea (“Under the Sea-Wind,” “The Sea Around Us,” “The Edge of the Sea”) and culminated with “Silent Spring,” a searing indictment of the misuse of chemicals by humans.

Lear’s meticulous research explains many previously unknown facts about Carson’s struggles as a writer, for it is a writer that Carson eventually became. Original scientific research was not Carson’s strongest suit, although she was sufficiently proficient to be granted a master’s degree in zoology from Johns Hopkins University. Writing accurately and passionately about the findings of science for a mass audience turned out to be her strength. How Carson found her true vocation is one of the most fascinating threads to follow in this book, of interest to any aspiring writer.

Her childhood on a 65-acre farm is not romanticized, nor is her family, one that would fit the mold of a dysfunctional family of the ’90s without any problem. Recognizing Rachel’s talents early, Carson’s mother, Maria Carson, stands like a bulwark between the family disasters and her youngest daughter, shielding her through most of her life. This biography is so rich one could focus on a pivotal figure, such as Maria Carson, and watch as her life unfolds in bas-relief against her daughter’s. As controlling as Maria Carson was, one wonders, after reading Lear’s book, if Carson would have been able to write the major works she did without the lifelong contributions and sacrifices of her mother — introducing her precocious daughter to nature’s wonders in their own back yard, selling chickens and teaching piano as a way to assist with college tuition, and doing housework and typing while Carson worked her way up the ladder at the U.S. Fish & Wildlife Service and wrote during the scraps of time available to her.

Rachel Carson’s domestic and financial responsibilities permeated most of her adult life. Despite unending hardships, Carson persisted. How she did this, who helped her along the way, what breaks and roadblocks she encountered, what it is that caught her eye and interested her enough to write about it, the decisions she made under duress, her triumphs and disappointments, and why she wrote the way she did — all of this is rich fodder for Lear’s historical research. Lear addresses topics that have not been fully explored until now, including why Carson came to Maine in the first place, why she never married, the depth of her ambition, and her inner sense of destiny. Carson thought of herself as “the sea’s biographer.” Amazingly, by the end of her relatively short life span, she was recognized in the United States and internationally as just that — and much more.

Several intriguing friendships stand out, in addition to the one with Dorothy Freeman: the relationship with her literary agent, Marie Rodell — quite a character in her own right; with illustrator Bob Hines, who would carry Carson out of the water when she stood in Maine tide pools too long; and with her mentor and biology Professor Mary Scott Skinker, whose troubled career as a gifted woman scientist merits the kind of careful attention given by Lear.

There is no question in my mind that Rachel Carson, had she lived to a ripe old age, would be following the controversies about deformed frogs in the Midwest, dioxin in Maine rivers or fish kills in Chesapeake Bay with keen interest and well-sharpened pencil. But it is up to the living — the writers of today — to carry on her legacy.

I was reading this biography on a porch in Canaan the other day when the wind shifted to the northwest, and the tops of the alders started to quiver. The man in my life turned to me and said that for years he used to feel depressed when the leaves started to fall, but he had a revelation one day looking out on the fields and woods that define his farm: The harsh winds are preparing the earth for spring by scattering the seed and providing a protective cover of leaves for winter. That simple thought had changed his feelings about the end of summer. I said, “That’s an observation Rachel Carson would have appreciated. You should read this book.”

Jennifer Wilder Logan organizd the 1989 memorial conference for Rachel Carson, convened on Southport Island to mark the 25th anniversary of Carson’s death on April 14, 1964, at the age of 56.