The surface was once the vast and serene land where human kind originated. Over time, many different species arrived and grew to coexist alongside humans until a great calamity of unknown origin caused the Surface to become near uninhabitable to most species. Humans and the like were then force to either leave or take their chances with the new and volatile energies that now permeated the land they called home. Those who left took to the Air-Currents, and those who stayed either died or 'evolved' into what are known today as Mutated Humans.
There are some areas located on the surface where the energy dissipated and are now somewhat inhabitable such as the Fryne Plains.