One of the first things you learn as you move up the ladder from "comic book reader" to "comic book collector" is that comics history is broken down into distinct categories, or "ages". The Golden Age began in 1938 with Action Comics #1 (you may have heard of it) and extended well into the 1950's. The Silver Age began in 1956 with DC's Showcase #4 (featuring a reimagined Flash character) and reinforced by Marvels's Fantastic Four #1 (1961). The Bronze Age began in...well...that one's a little tougher to establish. Generally understood to run from the early 1970's through the mid-80's, the Bronze Age doesn't have a specific "Genesis Moment" to announce its coming, though there were definite characters and trends collectors point to as indicators.
2. Speaking of chains, not to take anything away from Adams, but you can never go wrong with Superman busting out of chains. The iconic image has a pedigree going all the way back to Superman's earliest promo art, such as the seal for the "Supermen of America" fan club. Adams seems to acknowledge the roots of the image by giving Superman's face the somwhat squintier eyes and cheek line/dimple of Joe Shuster's Golden Age Superman. This nod to Superman's (then) 30+ years of history might have been reassuring in the midst of so much change and "social relevance" entering that era's comics.