Scilion

Scilion is a primordial world orbiting Alpha Centauri B.

Planetary habitability

Scilion had type of bacteria in it's oceans that slowly converted its thick CO₂ and Argon atmosphere to a more breathable one of Oxygen and Argon. Before it was turned into a poisonous atmosphere full of noxious fumes during the Scilion War

Post Scilion War

After the war the atmosphere slowly started to regenerate to it's former glory, but it's several thousands of years from recovering.