The Creatures That Time Forgot

First published in 1946 by Ray Bradbury, this short story (also known as Frost and Fire) follows Sim - a native of a planet whose inhabitants are fated to die after eight days from the deadly radiation that plaguing the land. His resolve steeled by memories inherited from his ancestors, Sim uses what little time he has left to venture out into the treacherous lands outside his people's caves, and seek out a band of scientists working to lengthen the planet's lifespan. Determined to reach his world's sole remaining rocket, despite the protests of all around him, he journeys across the land to find a way to extend his own life long enough to reach the last hope he has of escape... or die trying.