Earth

What We Know

 * Earth is in the Irken Database (The Nightmare Begins) before Zim arrives, but absent from the star charts.
 * Earth was represented by a sticky note added to the Star charts and was not named on the note (The Nightmare Begins)
 * Earth is not marked for conquest by the Irken Empire (Planet Jackers)
 * The episode 'Vindicated' shows us the date of Friday 10/7- Friday falls on October the Seventh on only a few dates such as 2016, 2022, 2033, 2039 and so forth.
 * The DVD Commentary states that the show is suppose to take place in an alternate reality where our present is more advanced technically but our society has largely degraded. The DVD was released in the early 2000s.

Pages regarding Earth

 * Nations of Earth

Earth in the Irken database, why?
Irken's discovered Earth long ago, which is why it's in the database of Zim's ship, and a sticky note on the star charts but did not at the time mark it for conquest- nor did they after Zim arrived as the Tallest didn't intend Zim to find the planet.

Earth is already conquered, but not by the Irken Empire
See: Ms. Bitters Is Not Human

This theory states that Earth has been taken over by a species so frightful to Irkens that their presence is only known perhaps to the Control Brain. Another is that this species is enigmatic and secretive and has done much to remain hidden from the Irken Empire. This is why Humans are so dumb in the series yet the technology so advanced.

Earth is already part of the Irken Empire
This theory states that Earth was long ago taken over by the Irkens and now provides food to Foodcourtia, but it was taken over in such away as to leave the people unaware of this. This is why Irkens and humans use the same computer operating system, and why the space program is defunded.