I did a quick google to see if I could come up with it, but what may be intersting is to compare the national (all NCAA teams factored in) average of yards per game or points per game for each year.
I had this discussion with a friend recently. With the increasing speed of the game, it's become more and more difficult to field a dominant defense. A great deal of defense has to do with reaction, and there is far less time to react to the offensive plays than there used to be. A defense stock loaded with smart, fast, physical guys is the only way to have a dominant D. Unfortunately there aren't too many programs with that sort of talent on D.