Mission of the Argo - Bob Springett - Bog

Generations have passed and there is still no sign of the Creators. Radio telescopes have provided no hints. Meanwhile rocketry has improved and there is now the technical feasibility of going out into deep space themselves. Further development in theoretical physics has also opened up the possibility of time travel, but this takes enormous energy and would destroy any life within a few light-hours, a radius the size of their Solar System. Even if the time travel option of going back to the First Parents is adopted, that will still require a deep-space capability as one of the steps.
Eventually the option of sliding back in time to meet the Creators is vetoed for political reasons. Instead, a generation starship is sent on a journey towards the most likely nearby star, a journey that will take longer than any of the crew expect to live. Their mission is to find the Creators and the descendants of the original crew are to report back to the home planet.
The mission finds Earth more than a thousand years after the runaway Greenhouse Effect has destroyed civilisation, and humans have been reduced back to migratory herding in northern Siberia. The Argo decides to slide back in time to prevent this disaster, but learns that this can't be done. Instead, they discover the Creators themselves were an engineered species. They slide back even further, only to
discover that they themselves created the Creators.