The 100 The 100 Series, Book 1.

Join one hundred teens on an epic journey from outer space to a barely recognizable Earth in this high-profile commercial teen series. In the future, humans live in city-like spaceships orbiting far above Earth's toxic atmosphere. No one knows when, or even if, the long-abandoned planet will be habitable again. But faced with dwindling resources and a growing populace, government leaders know they must reclaim their homeland-before it's too late....