The butterfly effect is the idea that small changes can have large effects. It is named after the scenario in Ray Bradbury's short story A Sound of Thunder, where a man steps on a butterfly in the past, and the future is dramatically changed.
On April 15, 1986, Marcus Irving travels to January 8, 19654 B.C. in his Yugo time machine, temporarily stranding Marty McFly and Doc Brown. They managed to escape sabre-tooth tigers shortly before Irving returned to bring them forward to 1997, as he was afraid of the butterfly effect their presence could cause that far in the past.
- Back to the Future (IDW Publishing)