Right now we're underground, but the surface of Sabra la Tau used to be populated by many different nations. As I said, the names of the current teams correspond to some of the nations that once existed. The Judges were the world's gods, and the oldest and most powerful of them were two known as the Old Man and the Old Woman. The Old Man is the earth we live in now, and the Old Woman was the sun.
From what I understand, the Old Woman became angry and the temperature started rising, bringing disaster to the world. The gods gathered everyone and told us to build a shelter that to keep us safe until the Old Woman calmed down. However, the shelter angered the Old Woman, I think...she tried to destroy it as the world burned, but the gods managed to seal the shelter and reinforce before she could.