Eight-hundred years ago, planet Atla was green, and its people were happy and thriving, until the day that the Smoke Stones began to fall from the sky. For fifty years, the mysterious black cubes rained down from space, soaking up breathable atmosphere and releasing a toxic fog that gathered and spread rapidly. Before long, the planet was wrapped in a smothering blanket of clouds, and the survivors took to calling their new home the Cloud Ocean. The capital city, Sky Island, was founded immediately after the Smoke Stones stopped falling nearly 700 years ago.