Pop Music - What is Pop?

Catherine and I began to do a timeline for the "History of Pop Music".
However, I noticed that the task was rather wide, as pop music could have began back when man was trying to create fire, could that be classed as popular music.
The guardian says in an article, "50 moments that shaped pop history" that the first moment to have changed pop history is 1954 - Elvis Presley records 'That's All Right Mama' at Sun Studios, Memphis.
However, I disagree. To know about the history of Pop Music, the definition has to be known. However, people's understanding of "pop" music, varies from background and opinion.
My understanding of Pop music is found the original abbreviation from "Popular Music" therefore I would say music in the top 40 today would be pop music, yet they can be sub classed into different genres. I also believe that Pop Music can be the Happy upbeat tunes generally performed by "One Hit Wonders" For example The Fast Food Rockers who dressed up in bright clothes and sang about there love of fast food chains.

There have been bands who make these happy upbeat songs, who have been labelled "Pop Bands" These usually consist of young either all girls or all boys, sometimes a mix, these members are young and attractive. Usually aimed at pre-teened girls. An example of this is Steps who had numerous hits like "Tragedy" cover of the Bee Gees original and 5,6,7,8.
They stayed around in the charts for the 90's then split in the early 00's. Which is stereotypical of the "Pop Band" label.