The Silver Age of Comic Books is considered to be roughly 1956-1970. It's open to opinion and debate as there is no official statement in the industry, aside from "Yeah, that sounds cool. Whatever."
In 1956, before Showcase introduced us to the new Flash, there were only 3 superheroes being regularly published: Superman, Batman and Wonder Woman. With the new Comics Code Authority (started in 1954) watching every page of every comic, publishers needed friendlier fare than the usual horror stories they were pumping out.
"Bah! I'm...what's the word I want? I'm zappingly surprised and disgusted! If only there was a word for it!"
Frederic Wertham (Boooooo!) decided that youth were becoming hooligans because of the influence of comic books. Despite the exact rise in shananagins matching the population growth, he decided it was comics that were ruining the country's impressionable youth. His lobbying is the reason for the Comics Code Authority, any publisher wanting to show that it was a readable book and 'mother approved', required this stamp to be featured on the cover:
Every book lovingly read and approved, I'm sure.
With this stamp, comics could continue bringing us such amazingly intriguing stories like these:
As if life wasn't fake enough with images from tv showing "golly gee" and "say, that's a swell idea" being regular daily conversation, kids got smacked in the face with purposely distracting portrayals of absolute evil. The Rainbow Raider, for example, wasn't an ice cream salesman, he was a supervillain!
Fathers, lock up your rainbows!
All you had to do in the 50's and 60's was barely finish a sentence and it was immediately transformed into a comic book story:
Writer: "Hey, what if Batman was - - "
Editor: "Brilliant!! Print it!!"
"I'm here to kick ass and shit my pants. And I already shit my pants."
So it's no surprise that the Silver Age harboured the introduction of literally hundreds of new heroes, villains, supporting characters and a whole buttload of characters and villains you will never see again for being so stupid.
The Silver Age gave us The Flash, Green Lantern, pretty much every Marvel character you see today and piles of hilarious comic book covers to search up on google for a good laugh every now and again (feel free to search up on google for a good laugh every now and again). There were a few characters in the DC Universe with the same names, which at some point, eventually, somebody noticed and thought it should be fixed somehow. The solution? They were from a different Earth! Just like this one! Except not this one! And Earth-2 and Earth-1 were born and decades of confusing continuity would ensue. Once these characters were finally seperated and existed in their own timeline, there was nothing better to do than to break down the barrier between them and have a good ol' fashioned team up! Sound like a long way to go to get back to square one? You're right!
There were many stories where DC heroes of Earth-1 had to warn the DC heroes of Earth-2 of some impending doom or needed their help with some impending doom of their own. There was always a reason for the team up, no matter how silly, and to break down the vibrational barrier of the two worlds was sometimes as simple as making a funny face and coughing three times. Thus Flash met Flash, Green Lantern met Green Lantern and Superman met an older Superman and I'm sure the "This one time..." stories went on into the wee morning hours.
By the time everyone figured out DC was running low on ideas, Marvel was ready to pick up the slack. Comic readers were older now and required a little bit more realistic heroes to read about. Along came self-doubting heroes who didn't know if they should bother helping others due to the fact that they might just screw it up. Not to mention their personal lives were just as important as their superhero lives.
Get over yourself, already.
Spider-Man was a huge, surprise hit, right off the bat. Everyone knows Spider-Man's origin as well as they know Superman's. Spidey has a personal drive to use his powers because of what happened the one time he didn't. Everyone can relate to that. Imagine if you didn't sleep with that girl from Dale's party and never got herpes. Wouldn't you use all your herpes power to help everyone else avoid that same disaster? Assuming the herpes were radioactive and gave you powers.
Another sellout was the disfunctional "Fantastic Four". Often seen bickering just as much as they were seen getting along, readers were shocked to see superheroes not complimenting each other while confidently saving the day with their amazing abilities. These new heroes were just like us: depressed, self-depricative and always screwing things up for themselves and everyone around them (I'm not the only one that does that, right?). Reed Richards was the distracted brainiac (allowing anything sci-fi to happen), Sue Storm was the hot blonde (necessary to get teen boys to buy the book), Johnny Storm was the teen flamer (not the way you're thinking) and Ben Grimm had his humanity covered by a monstrous appearance. Any one of them could have carried their own book at the time but teaming them up together was a direct reaction to DC's hot-selling team series Justice League of America.
But they were completely different kinds of stories.
In 1966, "Batman" hit the airwaves. With colorful sets, costumes and crazy comic book action, sales of the anything with a bat emblem on it skyrocketed faster than Adam West's ego. A new rush in sales hit every book that featured Batman and his boyfriend, Robin. This trickled down to other books as well, creating a huge sales boom for the next couple years.
In the late 60's, you could barely turn on your television box machine without seeing some kind of superhero in action. What a time to be a kid! Batman was fighting incredibly exciting villains such as Egghead and King Tut, while Spider-Man was swinging from cloud to cloud on his weblines!
"Hey kids! Physics is for losers!"
The Silver Age has no "official" ending as there is nobody keeping a master book of comic lore.
...and that is THE END of the Fantastic Four. Forever. Next issue: will Reed propose to Susan? Let's see!...
A few events are seen by many differing opinions as the end of the era:
1) The Death of Gwen Stacy - in one of the most memorable events in comic book history to this day, Spider-Man's girlfriend is killed...by Spider-Man. Though knocked of the Brooklyn Bridge by the Green Goblin, Spidey manages to catch her with a webline on her ankle. The sudden stop created something like this:
< - - - - - notice the little "SNAP" right by her head there? Oops. With great power comes the ability to kill people. This event was as if MJ's head exploded at the end of Spider-Man 2, imagine how surprised people would be. Those four little letters created a huge stir, and a rift, in the comic book community. One side were the "Snappies", the other side were the "A fall from that height would kill anyone-ees".
2) No more 12 cent comics - When this long-held price changed back in 1969, readers had to balance their budgets and beg for change on the streets to pay the extra few cents. Well, if we had a nickel for every time comic book prices went up, we'd have almost enough nickels to buy one comic book today!
3) Green Lantern's depression - Back when he started out, Hal Jordan was an optimistic renegade, ready to take the universe by it's green balls. By the end of the 60's, he was burned out, depressed and sucked dry of thrills. You've never seen such blue balls. As his sales plummeted, he was handed over to a new creative team of Denny O'Neil and Neal Adams, who took him in a different direction and teamed him with Green Arrow and sent them on a road trip or some shit.
In any case, there is certainly a few years around '69-'71 where everyone agrees The Silver Age ended and The Bronze Age began. We are currently in The Modern Age, though I'm not sure what that will be called once the present becomes the past and that name won't make any sense. Comic books continually re-invent themselves as fans become creators and those creators become editors-in-chief who piss off the fans.
Nothing we know today would exist if it weren't for The Silver Age of comic books, they propelled us into the future like The Flash punching you in the face, which Silver Age science taught me really works: