What thematic message does A Sound of Thunder and Jurassic Park have?

Time Travel, as presented in A Sound of Thunder and Jurassic Park, explores the idea of time travel as well as the possible repercussions of entering the past. Bradbury plays with the idea of "the ripple effect," noting even the smallest events in the past can have drastic repercussions on the future. The author's discussion of the ripple effect makes the reader consider his or her own place in the world, as well as their responsibilities for future generations.