While Primal Earth is the most Primal Element in WoW TBC Classic, farming this can still be worth it, since these elementals are more common as well. The lower competition means you can get more Primals per hour.
Farming Elemental Earth for gold at low levels
Elemental Earth is used primarily by Alchemists to make several kinds of potions. These Potions are much needed for Raids, which is why a single Elemental earth can sell for several gold. On my Server, I regularly sell my farmed Elemental Earth for 2g, and it sell very well at that price.
