The Earth of the Crossover world is, in essence, the same as the real world we all live in. Its history is the same, and its timeline will advance at the same rate as real time; if we hold an event in May and an event in June, roughly a month’s time will elapse on Crossover Earth between them. (Whether the same month’s time will elapse on Ariath is another matter.)
After play starts, Crossover Earth’s history will continue to play out as it does in the real world. If your character is from Earth, and spends time in both worlds, you’re free to have knowledge of anything happening on our real life Earth after game start, and you can expect Crossover Earth to remain consistent with it.
This means that players should not expect to affect the course of Crossover Earth’s history. There will be no way in play to, for instance, use Ariathan magic to prevent a war, or bring resources from Ariath to help starving nations. The focus of the campaign is on Ariath, and it would be too much work for staff to track and extrapolate an entire separate Earth history in addition to the game’s actual timeline.
Magic does not work on Crossover Earth, and neither do psionics, nanotech, or any other exotic skills found on Ariath. Earth is also not accommodating to people crossing over into it, and while it’s not totally impossible, Native Ariathans almost never find themselves on Earth; on those rare occasions that they do, it’s almost always an accident, and cannot be duplicated.
Most people from Crossover Earth have no idea that Ariath exists. If told about it, they would probably dismiss it as the stuff of fantasy novels. The few people who know about it are people who have actually visited there, who mostly keep it to themselves, and a tiny number of trusted people who they’ve told, and who have some reason not to assume they’re crazy.
Characters from Earth will be, as a rule, arriving in Ariath for the first time at game start. Most will never have heard of the place, and will have no idea what’s going on.
There are a great many ways to get to Ariath from Earth. Some people die on Earth and appear in Ariath, others sleep on Earth and dream their way across. Some people pass through mysterious doorways, or walk down forest paths, and don’t come out on Earth on the other side. We leave it to your creativity to invent your own method of crossing over.
Depending on how your character got to Ariath, you may or may not be able to return to Earth between events. Characters who died on Earth usually cannot, while dreamers often awake after a few days in Ariath and find themselves in their beds at home.
All characters coming to Ariath from Earth will be human in origin, but that does not necessarily mean they will remain that way. On occasion, the transition changes people as they cross. So, if you want to play someone from Earth, but want to have knowledge of magic when you arrive, or want your character to mysteriously be a goblin or minotaur on arrival, feel free! Being from Earth need not restrict your character’s skills or race while in the game world.