The way you describe it, it would seem to be Natural origin - there are no other influences except the person's own dedication and focus that creates the connection to the earth.
Alternately you could go Magic, if there is some kind of magical connection to the earth that is formed by such training.
Either one works.
"Shut up Mr. Burton, you are not brought upon this world to get it!" - Lo Pan
@MadGremlin
I have created my own character who is a "Monk" of Boulder, basically a group of devout Martial Artists who train religious, slowly becoming one with the earth through meditation and fasting. After 10 years of training a monk of boulder is finnaly ready to serve the earth. What origin would this be, by the way the powers of a Monk of Boulder are Rock Armor/Energy Fist