The Earth-class colony ships were read about in Forerunner terminals by modern UNSC Marines. The Earth-class colony ship was designed for colonization of planets in the later history of Ancient Humans, and resemble simple UNSC Colony ships, just outfitted with light sheilds, and much more advanced avionics. They had no weapons, so they were considered obsolete as colonization would not work as the Flood was taking over worlds faster then a Colony ship could get through a single slipspace jump. One ship was saved from the Scrapyard, the Obliretian Tera. The Obliretian Tera was destroyed when the Forerunners destroyed the ancient humans, and backtracked there techology back to simple hunter-gatherers. The Earth-class ships were never designed for atmospheric entry or flight.