I'm writting a novel (in Spanish, I'm from Chile) based on Sumerian culture separated in two periods (Present & Future).
Present: archaeologists find some new sumerian stone tablets that hide great scientific data, religions try to boicot the investigation, scientists escape to space thanks to the discovery and leave Earth behind.
Future: many years in search of a new Earth-like planet, they find one, some kind of alien race communicates with humans, help them to find their way and to rise a new human culture.
Problem is I don't know how to join both sides of the story. I know that I have some pre-constructed ressources like space-odissey, or the build of the main character, or just let a blank part (undisclosed) and describe maybe the alien race experience in that time period.
What's the best way to bridge a large time gap in science-fiction?