Wow. This is a milestone. So many of us who became teenagers in the early 60s were really into the whole folk revival—and Peter, Paul, and Mary was absolutely the dominant public image of that revival.
They took the progressive G.I. (born 1901-1924) folk movement (The Weavers, Woodie Guthrie, Pete Seeger et al.) and culturally radicalized it so that it hit the sweet spot for first-wave Boomer (born 1943-1960). But they were also basically mild mannered—never extreme, unpleasant, or confrontational. Their harmonies were never atonal. They were the most popular “beatniks” ever to perform for the public. The bio points out another Silent (born 1925-1942) dimension to her life story: four marriages.