SAN FRANCISCO — Facebook on Thursday began transforming profile pages into interactive digital scrap books that let members of the world’s leading online social network tell the stories of their lives. The “Timeline” design rolled out on Thursday was unveiled at a Facebook developers conference in September came with a new class of “open graph” applications that let people discover and share music, movies, books and news. “Timeline gives you an easy way to rediscover the things you shared, and collect your most important moments,” Facebook said in a blog post announcing that the change is available to its more than 800 million members. “It also lets you share new experiences, like the music you listen to or the miles you run.” Timeline visually graphs Facebook posts based on when they were uploaded, letting people look back at pictures from special events, memorialized accomplishments, pithy text exchanges and other posts from various points in their lives. After upgrading to Timeline, people will have seven days to privately review and edit how it will be viewable by friends at the social network before it automatically goes live online. “Your new timeline will replace your profile, but all your stories and photos will still be there,” Facebook said. Tools allow Facebook users to hide posts they don’t want included in timelines or change settings regarding which of their friends or associates can see posts.