What are some of the earliest examples of chord tones like dominant sevenths and ninths being used? I am trying to determine how basic harmonic music forms evolved toward forms such as Blues and Jazz.
If you Google dominant seventh and ninth chords wikipedia gives a good overview of the early usage of those, i.e., they did appear in classical music. This wasn't obvious perhaps, since the classical composers used those chords as harmonic devices among many others, where their use in blues is pretty insistent.
As far as harmonic forms, I believe harmonic music was really a move from monophonic music as polyphony became so intricate (in for example the 16th century or thereabouts) that the many separate melodies met so frequently that consciousness of harmonic consonance was more or less forced upon the composers and the hearers. This was made possible by advances in the construction of scale intervals (e.g. equal temperament) such that true harmonies could occur. To the Greeks, for example, a third was considered a dissonance and it in fact was because of the construction of their intervals.
If you consider the driving force for a composition, I personally would consider 19th century and folks like Claude Debussy as examples of using harmonic complexity and subtlety rather than melody predominantly. That tendency was carried to almost incomprehensible (to the ear and emotion) lengths in 20th century jazz.
I don't personally consider blues to have originated in harmonic considerations. It appears to me to have been the interaction of the African vocal inflection capability with Protestant gospel forms in the American South, and perhaps some cross-breeding with Appalachian Celtic roots with benefit to both. It seems more a melody form, in other words, where the method boils down to adding a minor third, an augmented 4th and a minor 7th to the vocal possibilites (in embellishment of the basic gospel I IV V). For example in key of C, use of Eb, F# and Bb (notes, not chords necessarily).
Having just watched Ken Burns' Jazz series recently, the evolution of jazz in New Orleans is fresh in my mind. I think the jazz that evolved there, culminating in Louis Armstrong and others of the early part of the 20th century, in large part out of the virtuosity of the players, using the available forms. We forget that much of the great classical music was composed and has come down to us from virtuoso players that had a tremendous skill on their instruments and ability to improvise (J.S. Bach on piano and organ, Mozart on piano, Beethoven on piano, etc.). This occurred again in New Orleans, 20th century.
I hope this is useful as a departure point for discussion (this is off the top of my head; to attack the matter rigorously with cites to original music and authority would be a major piece of resarch work).