Consider the impact of seemingly inconsequential events. The prolific sci-fi author, Isaac Asimov, wrote a short story chronicling a time traveler who, back in the age of dinosaurs, stepped off the path and inadvertently killed an insect.
When the traveler returned to the present time, language and the environment had changed. The insect was food for another creature, which consequently starved, and so on cascading through the eons. The eventual impact was catastrophic.