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I heard that rock was created from blues. But most of the scales in rock are either major or minor. But blues scales are created from adding chromatic notes to a pentatonic scale.
Isn't rock more similar to say classical or pop music since they both share the same regular major/minor scales?
'Rock' is an umbrella term referring to an area of music containing many sub-genres that has been evolving for nearly 70 years now. Even at its birth, it evolved from multiple genres such as Country, Blues, and Boogie-Woogie piano music. As time has moved on it has taken in more and more influcences such as folk, classical, jazz... and ultimately, every other genre out there. Accordingly, it has incorporated harmonic pallettes from all those styles - and in some ways, found ways to fuse them together.
most of the scales in rock are either major or minor
First, a question - where does that assertion come from? is it your impression or does it come from a statistical analysis of a corpus of work?
Doubtless there is a lot of rock music that is based on major and minor scales. There's also an awful lot that is based around the blues scale - I bet if you asked 10 guitarists to play a 'rock riff', more than half would play something based around a blues scale. There are a lot of modal influences in rock too. (I've sometimes thought that there seems to be a kind of 'Rock scale' or 'rock key' that incorporates aspects of Major, blues, minor, and perhaps the Mixolydian mode.)
As an illustration of something that exhibits a kind of bluesy rock tonality, Have a listen to Joe's Garage. The first part is fairly straightforward major - then pay attention to what happens at about 4 minutes, when they're making it sound more 'rocky'. They're certainly not sticking to straightforward major - or minor - at that point.
blues scales are created from adding chromatic notes to a pentatonic scale.
It's not as simple as that. The archetypal blues sound is all about bending notes through ranges of pitch (which you can hear a little of in the Joe's Garage vocal). There are simplified versions of the blues scale which could be described in the way you have, but that wouldn't qualify as a full description of classic blues tonality.
Isn't rock more similar to say classical or pop music
Maybe - but only in that rock, pop, and classical are all huge, sprawling families of genres that have adopted many different influences over the years, and include examples using many different types of scale.
This is a style question, not really a theory question.
Let's skip the discussion about blues scale versus blue notes, blues harmony, and what is rock tonality.
The question is...
...how is rock founded from blues
The easiest, most direct answer I can think of is: Joe Turner and Bib Mama Thornton.
The Rock & Roll versions are:
Initially rock was just blues (performed by whites) with a different performance style. Regarding scales and harmony there is no difference in the 'blues' and early 'rock and roll'.
...But most of the scales in rock are either major or minor...
Rock is too broad a label for this question. We can go from Slayer to Elvis under the rock umbrella! It's like lumping Turlough O'Carolan and J.S. Bach in the same category, because both used major scales and lived during the same time period. Try to differentiate what style of rock you are talking about.
This is "rock" when blues is removed...
EDIT
You mention blues, rock, pop, & classical and are looking at similarities and differences. All of them share a commonality which is the diatonic scale (yes, it applies to blues.) In terms of history and evolution of styles you should consider how the hymn is a foundation. In America it becomes the spiritual. Also the waltz and late 19th century/early 20th century sheet music songs are the ancestor of pop. In both cases, hymns and waltzes, the diatonic scale is the foundation. Other styles evolved from them. Instead of make scale/style associates think about harmony and overlapping, evolving styles.
To be extremely unacademic, in my head I consider the blues scale to be the "cool" scale. Whenever I hear it used in a song, it just makes the song sound and feel "cool." It adds fun, with just a slight bit of edge (owing to that dissonant tritone). Be it the Contra Base theme or Black Dog by Zeppelin
For some basics, the blues scale is the pentatonic minor (5 notes from the 7 in a minor scale) with a few extra notes, the blues notes, added. (I don't know if that's the actual name, but I call it that since it's what makes the blues scale the blues scale; hearing them is what gives it that sound). They are 3 chromatic notes--the fourth, the augmented fourth/diminished fifth (aka tritone), and the fifth.
Obviously, this scale was originally used in, you guessed it, the blues. Chuck Berry is the father of rock 'n' roll, and some of his most famous riffs and licks became trademark staples of rock guitar. Listen to his legendary "Johnny B Goode" or the equally iconic "Tutti Frutti" by Little Richard. These songs are on the border where blues first became rock 'n' roll. Then listen to songs like Steppenwolf's "Born to Be Wild" and Sweet's Ballroom Blitz. You can hear the similar riffs used in these songs, the same Chuck Berry thing where the guitars play a power chord (fifth), then hammer on a sixth and augmented sixth. This sort of thing is still used way into the 90s you can hear it in Alice in Chains' Man in the Box (albeit it's more subtle there). One of the most common Chuck Berry licks used all the time in rock and metal is doing a unison bend on the root note and then hitting its fifth on the string above it. The most obvious example that comes to mind is the solo on KISS' "Rock 'N Roll All Nite"
Another trademark of rock music that comes from the blues is the 12 bar blues progression (i.e. 4 bars of I, then 4 bars of IV, 2 again of I, 2 bars of V, and then repeat.) E.g. Rock 'N Roll - Led Zeppelin
Historically speaking too, most of the great rock musicians of the 60s were inspired by the blues players of the 50s. Mick Jagger is the original rock frontman, and he modeled his style after the black American blues players. The Stones are, after all, a blues rock band. The Beatles too.
Of course, rock eventually diverged and began incorporating everything else--minor, harmonic minor, major, modes of major scale, exotic scales in metal, jazz, you name it. But it began in the blues, and at the very heart of a rock song is usually the blues scale somewhere in there, be it the main riff or at the very least some licks in the lead playing. Kirk Hammett and Dave Mustaine for e.g. use blues licks in their solos all the time. The solo for the Mechanix comes to mind, and I'm pretty sure nearly all the songs on Kill 'Em All are based around either pentatonic or blues riffs. It would be quite rare to find any modern rock or metal song without any influence from the blues. Historically and culturally too, it was the blues players that became and inspired the original generation of rock 'n' roll.
My take on this question is that it seems to me that the term "Blues" is rather loosely applied to a lot of music that has it's origins further back in history, such as "Negro Spiritual" and even further back than that in "Jungle rhythm". Both of these categories are often found in "Blues" and in early and even current "Rock" music. When I hear someone say Rock came from "Blues" or Rock came from "Country", it always sounds to me like one genre is trying to steal the thunder from another genre, and I try to disregard it. I prefer to just appreciate each classification, whatever it may be, for the way it makes me feel when I listen or play it. Also, it occurs to me that the major scale or the blues scale is only a part of what makes rock a separate category, there's also the rhythm, the lyric, the "attitude", all often very similar in nature to Blues, and Country, and just about anything else we've ever heard. I understand that it's important to know the history, but in this case the history doesn't seem to be helping one to understand the music and may be confusing the issue. My impulse is to just accept it for what it is.
