Eras are what's known as resets, don't happen often but do happen to give new players a chance to become top players.
Eras end when all Bosses (including SpaceHunter Boss at coordinates
0x0) are beaten, after that, a grace period of a few days is given for all players to go mayhem and have fun without repercussions, just before the reset and beginning of the new Era.
A reset means that everything is restored to the beginning: Bosses, guilds, user scores, resources, units, buildings, missions, research levels… Resets are a good opportunity for new features and gameplay improvements and balancing to be introduced.
Why Resets? They provide a chance for new players to reach the top rankings and for all players to start fresh and form new alliances, strategies and more.
These are the current game Eras:
The first Era of the game. Expect for a lot of things to change in order to balance the game as days go by, and for new features being added or changed.
Here's how the Universe ended:
Era 2 is currently active!