the salt of the earth

     The phrase "salt of the earth" is often used to mean the plain ordinary folks who do most of the physical work of the planet. At least, that's how the "salt of the earth" describe themselves. I'm not sure "the salt of the earth" was originally meant as a compliment. We get salt from salt water or from salt mines. The mines are under the earth. Hmm. No that's not it. If you put salt on the earth, nothing will grow there again, perhaps for hundreds of years, as the  Romans salted the fields of Carthage after defeating them in a war. That could be it. "The salt of the earth" may mean the people who are determined to render the earth into a desert, or a wasteland.