Planet Earth (1974) represents creator Gene Roddenberry's second effort to get his Genesis II (1973) series premise aired on American network television.
As you may remember, Genesis II concerned a 20th century scientist, Dylan Hunt (Alex Cord) awaking in 2133 AD and helping the pacifist organization called PAX (Latin for peace) restore the "best of the past" while ignoring "the worst."
Because of his 20th century knowledge and know-how (and because of a system of sub-shuttles "honeycombing" the post-apocalyptic world...), Dylan proved a perfect "agent" of PAX to accomplish this critical mission of planetary reconstruction (think Irish monks in the Dark Ages...). Still, Dylan Hunt had to overcome his own twentieth century addiction to violence and killing.
In Genesis II, the people of PAX wore simple garments and looked like Roman slaves. In Planet Earth, the people of PAX wear form-fitting and futuristic uniforms that are brightly reminiscent of Star Trek.
In Genesis II, PAX had no advanced technology or advanced medicine. By contrast, Planet Earth reveals a PAX replete with handheld computers, view-screens and large computer banks. The people of PAX are also more knowledgeable here, and there are doctors available who can perform advanced "bioplastic" heart surgery. These changes reveal a completely made-over PAX, one which (like the United Federation of Planets) represents a virtual utopia.