The end of the Golden Age of man was marked by massive world war. A war larger and more destructive than any that had come before. With the use of super-men, machines of war, giant robots, laser weapons, particle cannons, millions upon millions were killed. With the killing of a living creature, it's PPE is released to the environment. Normally, this energy will dissipate and maybe have minor lingering effects (poltergeist, ghosts, strange feelings when in a location), or typically no lingering effects at all.