Earth

It should be clear what planet Earth is; home to mankind, in a time of technological advancement. Earth is also the home planet of Lord British and the Avatar. However, Earth itself plays a minor role in the series. It is usually only seen in the intro and end sequences of the games.

In Ultima II however, Earth is the central place of the game. Minax had manipulated the timeline, resulting in a totally changed past. In the end, Earth was destroyed by a nuclear holocaust - the Aftermath - in 2111 A.D.. The Stranger attempted to repair the damage to the timeline, traveling to these periods of time, which were totally changed by Minax' meddling:


 * Pangea - 9 million B.C.
 * 1423 B.C.
 * 1990 A.D.
 * Aftermath - 2112 A.D.

In the end, the timeline was returned to normal, and all these events had never happened, apart from the memories of the Stranger.

The only other game where Earth is part of the game itself is Ultima IX, as it is the first playable area of the game. The Avatar gets to do some training and interacts with the Gypsy before arriving in Britannia.

Places
During the time twisting of Ultima II, there were three places of interest, besides the castle of Lord British:


 * New San Antonio in 1990 A.D.
 * Pirate Harbour in 2112 A.D. Aftermath
 * Port Bonifice in 1990 A.D.

Trivia

 * The coordinates for Earth in Ultima II are 6,6,6. (Interestingly, this is the famous number of the Devil. Make of it what you want...)
 * The valley of Eodon is actually on Earth, but totally out of phase, so it can be only reached with the Orb of the Moons.
 * If you want to cheat in Ultima IX, Earth is the location of the "in game" cheats (they're over the fence from where you practice with your sword).