If the length of copyright terms are "life of the author plus 70 years", try to imagine the effect on the public domain if the average lifespan of a person becomes at least 120 years.
With that in mind, check out this science fiction short story entitled "Melancholy Elephants" (which was apparently written back in the day when copyright terms were "merely" the life of the author plus 50 years).
Fight the future...