What is the importance of the setting in "A Sound of Thunder"?

Setting is of great importance in "A Sound of Thunder" both because of the direct danger the setting poses to the characters, and to the ability of the setting to affect the flow of history.

The characters are engaged in a time safari - using a time machine to travel to the distant past in order to hunt animals that are extinct in the modern era. In this particular case, they are hunting a tyrannosaur,...

Setting is of great importance in "A Sound of Thunder" both because of the direct danger the setting poses to the characters, and to the ability of the setting to affect the flow of history.

The characters are engaged in a time safari - using a time machine to travel to the distant past in order to hunt animals that are extinct in the modern era. In this particular case, they are hunting a tyrannosaur, so their trip, and its setting, necessarily preclude any possibility of assistance. If anything goes wrong or anyone is injured or killed, their only option is to retreat to the machine and return to their own time.

Furthermore, the setting is important because influencing it in any way may have unforeseen effects upon the way that history plays out, as the characters know it. This means that any change or interaction with the setting, no matter how small, might alter the way life on Earth plays out; they could inadvertently cause the extinction of humanity through some innocuous action. This is demonstrated at the end of the story, when Eckels accidentally kills a butterfly, resulting in the world that they return to being different from the one they left.