After the early rise of superheroes as a dominant theme in the medium of comics during the Golden Age of Comics, the outlook of the medium changed its dominant themes in the 1950s. While the major heroes maintained a degree of popularity, their widespread exposure over the medium changed, as different themes became more relevant and became better-selling than the heroes who had helped to popularize the medium.
The rise of this so-called "Atomic Age" was due to many factors. Primary among them was the development of the knowledge concerning nuclear fission, the use of atomic weapons at the close of the Second World War in Japan, and the inception of the nuclear arms race (also known as atomic weapons) between the USA and the USSR. With its vast potential for destruction as well as a poor understanding of the energies released during fission, nuclear (or atomic) energy came to the forefront of the public's interest, both in awe and in fear of its potential.
The decline of the superhero can be tied to other factors as well. While many other heroes were introduced in the Golden Age, the primary five could be said to be Superman, Batman, Captain America, Wonder Woman and Captain Marvel. A common theme among these early heroes was the their opposition to the forces of the Axis in the Second World War. Reading these comics thus served as a form of patriotism, and without this interest, the medium adapted to new concerns in society.
The introduction of the 1954 book Seduction of the Innocent, also helped to dissuade the general populace from reading superhero comics. This book raised many tenuous critiscims regarding the medium, many of which were tied very loosely to fears over the spread of homosexuality through its normalization in the actions of characters, and resulted in a moral panic about the effects of the medium. The Comics Code Authority subsequently assuaged the fears of parents over the medium, but also curtailed many of the common themes previously seen in comics, which helped science fiction replace horror as a dominant feature in the medium.
An additional development was the use of the long range rockets during the Second World War. Originally developed by Wernher Von Braun, it quickly became apparent after the end of the Second World War that such technology could be used for space exploration. While space exploration had been a stapled of earlier science fiction, for the first time there existed a means by which man might legitimately be able to explore the cosmos.
A dominant factor inside of the medium of comics in these years were the space serials. With such titles as Mystery in Space or Strange Adventures, the medium began to explore themes dealing with science fiction, many of them dealing with mankind visiting the planets, or with some form of first contact occurring between man and aliens. Long running series such as Journey Into Mystery (from Atlas Comics, a precursor to Marvel Comics), which had started off as a horror anthology later changed its content to mirror those of other comics, and focused instead on these same science fiction concepts. The few new major superheroes of this period often had a science fiction element, and highlighted these same themes. Adam Strange and Captain Comet were regular men who were taken to space and who partook in adventures. The Martian Manhunter was a martian living among humans, similar in a sense to many alien invasion plots, where the aliens were already among us. The Legion of Super Heroes represented the effects of the change of the medium on the mainstream superheroes as Superboy traveled to the future to meet humans who had explored the cosmos.
The era also directly influenced the language used in the creation of comics. As author Alan Sillitoe described in his novel "Saturday Night, Sunday Morning" people in this era were living under the "long shadow of the bomb" and this same focus was used in comics. For instance, a common word used across many titles at the time was "Doom" which would provide an easy way to catch the eye for people who were living in the 1950s under the constant threat of nuclear war in a renewed World War.
The Atomic Age of Comics is one which is still argued about among comic historians. Some see it as nothing more than exhibiting trends among readers in the golden age, but others regard it as an age unto itself, distinctly different from golden age comics, but not yet quite to the Silver Age. Indeed there are many ties to the Silver Age within the Atomic Age. A few of DC's silver age heroes (Barry Allen and Hal Jordan) were rebooted versions of older heroes with a more modern science spin. Also a few of the early silver age characters utilized common words to the Atomic such as "Doom" in the case of the Doom Patrol and Doctor Doom.
The end of the Atomic Age of Comics can be tied primarily to the rise of Silver Age heroes. It eventually came to be that those wanting to write superhero stories learned the lessons of the changing medium and incorporated in a more scientific approach to their characters. New characters such as Spider-Man, Iron Man and the Fantastic Four exhibited a new focus on science for the superheroes, and other heroes such as Hawkman were relaunched with a science fiction and space based background. Additionally the Space Race between the USA and the USSR gave comic readers real life heroes to watch as opposed to the heroes of science fiction, and thus as real life imitated art, there became less interest in the fictional exploits of spacemen as opposed to the real life heroes.