Complex sentence: Spaceship Earth was originally sponsored by the Bell System from 1982 until 1984, when it was broken into smaller companies in 1984, and its parent company, AT&T, became an independent company.
Split into simpler sentences: Spaceship Earth was sponsored by the Bell System originally, from 1982 until 1984. Bell was broken up into smaller companies in 1984, and its parent company, AT&T became its own independent company.