Answer by Jon Mixon:
Michael Jackson was 21 years old when Off the Wall, what would have been the most popular album during the entirety of the 1980s was released. That album sold 8 million copes alone (and more since that time) in an era where music videos were in their infancy and Jackson was blocked from performing on many networks and in certain venues due to his race. Bieber (who is now 21), on the other hand (as of 2012) has sold 11 million CDs TOTAL in the United States. with a total of 25 million sold worldwide.
Just two years later Jackson, at 23, released Thriller which was (and remains) the largest selling album by a single performer in the history of modern music. It has sold at least 51-65 million copies (as of 2013) and was for the years of 1982 and 1983 the best selling album in the music industry. That means just for Thriller alone, Michael sold 2 1/2 times as many albums than Bieber has for his entire career.
There's no need to delve into Jackson's lackluster Bad release in 1987 which sold a "paltry" 8 million albums as it is clear that Jackson was a bigger star even in an era without Internet streaming, YouTube or TMZ to record his every utterance and performance. In less than 10 years (1980-1989) Jackson sold a total of 41 million albums (if we just go with the numbers sold during that timespan)
Bieber's success is viewed as being "big" now because the music industry itself has shrank significantly. Jackson's success came at a time when the industry was dominant.
Winner: Michael Jackson.