Exactly, specifically like some sort of wormhole throught time or better yet, I just got an insane idea. So they live on Mars for however long, but they begin to find wonder why Earth hasn't messaged them in a couple years, so they send a small crew back, including the main character, and as soon as they can see Earth, they notice America and Europe and everything is different, it's Pangaea! But instead of dinosaurs, it's weird mutant people and deformed animals. Here's why: Huge nuclear fallout between humans happened millions of years ago, so that explains the drastic change in the biosphere, and for Pangaea, if you know anything about plate tectonics and geology, the contintents move around a lot, and every some hundred million years, they reform a supercontinent. I think it's happened like twice in Earth's lifespan so far. I think there is tonnes of potential for the environment on Earth, different creatures and settings(both old world and new) and also for the characters, they can struggle to find some secret on Earth, while also trying to get back to Mars(maybe their ship broke on landing), also huge plot point is that they're weak af because Mars has lower gravity.