Is there some sort of way our characters got to the spiral, in the Arcanum, I'm PREEEETY sure one person said our wizard is from earth, 2 questions. HOW did we get there, and WILL there be an Earth spiral door?
When we first create a wizard, there's a conversation between Ambrose and Gamma the owl. Ambrose says something like "it's working, we found them!" and Gamma says, "Whoooo?" And, it's us. Ambrose says we come from "another world, one that doesn't even believe in magic." He seems to be peering down into a crystal ball. So right from the start, it's implied that we're from Earth.
Next thing we know, we're in his office and there's no explanation given for how we got there. Somehow we've arrived and this is the point where he asks us what we look like, etc.
Some worlds on the spiral have missing keys - for example, we're told at the start of our Celestian quest that their key was missing for a long time and only recently found. Also, I think we have to actually make a key for Khrysalis. In part of the Marleybone lore, we're told Harold Digmoore read an ancient incantation and found himself in Wizard City. Before that, the Marleybonians didn't believe in the existence of the Spiral, or magic. Maybe Earth is a world like Marleybone was, one that has lost its key and therefore it's cut off from the spiral and the knowledge of magic.
That idea still doesn't answer how we get from Earth to Ambrose, though. I don't know. Maybe Ambrose spoke the same magic incantation that Harold Digmoore did. Or, maybe Grandmother Raven had something to do with it.