Terra Nova 

Terra Nova means “New Land” in Latin and is the name of one of the first Earth colonies created on an alien planet colonized before fast interstellar travel was possible. After the colonists settled down, they refused to allow more colonists to land. All contact with the colony was lost shortly after that and no investigation team was ever sent. The Enterprise investigates the fate of the colonists. When they arrive, they find descendents of the colonists who have become more alien than could ever have imagined. is taken hostage and in the process of trying to establish an understanding with the colonists, who call themselves Novans, they discover a meteor crashed into the Northern hemisphere causing poisonous gas to spread killing the adults. Only children young enough to adapt survived, but the build-up of toxins in the water supply over the years will kill them all unless they leave the planet or relocate to the unaffected Southern hemisphere.