The.100.S04E09.720p.English-

Set in 2149, 97 years after a nuclear apocalypse has devastated the surface of Earth, the only survivors were approximately 400 inhabitants of 12 national space stations that were in orbit at the time. Three generations have survived in space. The Ark has strict measures, including capital punishment for those over 18 and population control, as the leaders of the Ark take steps to ensure the survival of the human race. But now, resources are running out and the Ark is dying. For the first time in nearly a century, there is talk of returning to Earth.
100 juveniles convicted of various crimes are sent to Earth to see if it is survivable. Among them are 17-year-old Clarke Griffin, the daughter of the Ark's chief medical officer and of the Ark's chief engineer; Wells Jaha, the son of Chancellor Jaha; the daredevil Finn Collins; the illegal sister Octavia Blake; her stowaway brother Bellamy Blake; the lighthearted Jasper Jordan; and the resourceful Monty Green.
Technologically blind to what’s happening to the 100 on Earth, the Ark’s leaders Chancellor Jaha, second-in-command Marcus Kane, Councilwoman Abigail Griffin and the Council are faced with difficult decisions about life, death and the continued existence of the human race.
For the 100, Earth is an alien planet; however, they quickly discover that Earth is filled with new wonders and dangers of all sorts. Then, they discover that not all humanity was wiped out, and some survived the nuclear apocalypse: the Grounders, who live in 12 clans locked in a power struggle; the Reapers, another group of Grounders who have become cannibals; and the Mountain Men, who live in Mount Weather and locked themselves away before the apocalypse.
n the fourth season, two dozen nuclear reactors around the world are melting down due to decades of neglect that will result in the majority of the planet becoming uninhabitable. Clarke and the others investigate ways to survive the coming wave of radiation that will result in the second nuclear apocalypse. When it is discovered that Nightbloods have a higher resistance to radiation, Clarke and the others attempt to recreate the serum but fail to test it. An old bunker is discovered that can protect 1200 people for five years. Twelve Champions fight in the Final Conclave to determine control of the bunker. Octavia wins and decides that each of the twelve clans receive a hundred spots in the bunker, uniting everyone into a single clan called Wonkru. Bellamy and six others return to space to live in the remnants of the original Ark while Clarke, who is now a Nightblood, remains on the ground.