Written by Howard Zahniser—who died of a heart attack at age 58 four months before the bill was signed into law— the legislation authorized the United States Congress to set aside a total of 9 million acres in selected areas in the national forests, national parks, national wildlife refuges, and other federal lands as units to be kept permanently unchanged by humans. It also provided for more acreage to be designated as wilderness for preservation. In defining wilderness, Zahniser invoked Marshall and his contemporaries, stating that "in contrast with those areas where man and his own works dominate the landscape, is hereby recognized as an area where the earth and its community of life are untrammeled by man, where man himself is a visitor who does not remain." The act's signing was the most important event in the history of The Wilderness Society; members Mardy Murie and Alice Zahniser stood beside Johnson as he signed the legislation. With the Wilderness Act, the United States guaranteed permanent protection of wild and scenic natural areas for future generations.