So I'm currently engulfed in a dilemma regarding the timeline of my graphic novel. My original plan was to have the first three or four books take place in a fantasy world, then the following three or four books explore the same world thousands of years in the past in a previous era of civilization. The plots are interconnected, but I'm worried that the difference in atmosphere and setting would be too great to pull off effectively. The two eras are completely different in terms of technology, settlement, and culture, but the events in the earlier timeline are directly connected to and acutely influence the events in the later one. The main character from the later time period is sent back through time to prevent a catastrophe, but I'm wondering if the readers will accept such a huge change. Here are my main questions: Is jumping through time to tell more of the story a valid tactic, when the two eras being written about differ completely? If it is valid, then what sort of problems might I run into when making the transition and how might I avoid them?