History of Earth Two

One green tinted planet in the center of the screen seems to pinpoint itself by its position and growth as THE planet. And what we see looks to be Earth... clearly... incredibly... an exact duplicate of our planet...

It is the homeworld of the Earth Two natives, a pre-warp humanoid species, that had been reduced to a subset known as the Onlies. The entire adult population of the planet (referred to as "Grups" by the Onlies) was killed in a failed microbiological life prolongation experiment.

After discovering a cure for the virus and gaining the trust of the Onlies, the Enterprise arranged with Starfleet for teachers and advisors to be sent to this planet so they could aid them in rebuilding their civilization.

Miri is a native of the planet. Jahn is the leader of the Onlies. Louise was a young woman from the planet infected with the virus. Louise was only a little bit older than Miri.