The First Crossing refers to the 15-year jouney from Earth to Pern. Most of the colonists were in suspended animation for the entire 15-year trip. The crew of the colony ships were awake for 5-year shifts, and asleep the other 10. Along with humans, seeds and certain animals were brought, along with a large genetic database and frozen ova and sperm. The animals brought were used to incubate the engineered ova.