Life spores were living things from which more complex life would develop. They were developed by the Olympians.
Prometheus stole life spores from the temple on Olympus and scattered them across the universe, creating life. This angered Zeus, who banished him to be chained to a mountain on a planet for the rest of his existence.
Eventually, Prometheus returned to Olympus with the Fourth Doctor and K9 Mark II, by which time life in the universe had died out. Zeus intended to wait until the life spores were perfected and would only produce peaceful creatures before recreating life. However, Prometheus again stole life spores and escaped with the Doctor and K9 in the TARDIS, planning to again scatter them across the universe. (COMIC: The Life Bringer)