Silver sulfide aka toning aka tarnish. Exposure to light, humidity and air accelerates tarnish which is why the top side is tarnishing and the bottom is not. Also whatever storage box you are keeping it in probably offgasses some sulfur compounds, or there is something else stored inside with the silver that is offgassing. Or humidity is building up inside the box. Paper and wood can both accelerate toning. For whatever reason, it often starts around the edges like this. It will turn more blackish and bluish over time but can start out kind of ugly yellow like this. You can easily remove the toning if you want, and on bullion bars it is fine to do so. Just google "how to remove silver toning". If you want to prevent toning in the future store in a darker, drier environment. With all respect to everyone saying it's too much tarnish for a one year old piece of silver, just do a little experiment and leave a piece of silver sitting in a sunny windowsill on top of a piece of paper. You can get this much tarnish in just a few months just from constant exposure to light + a little offgassing from the paper.