Primal Earth Farming
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.
As with all the Primal Elements, Primal Earth is created by combining 10 Mote of Earth. Any Earth Elemental in the Outlands can drop 1-2 of these Motes. In addition to this, Motes of Earth are also commonly found by Miners in Outland mining nodes.
Nagrand Primal Earth farming
Netherstorm Primal Earth Farming
Around the edges of the floating Islands of Netherstorm, there are a bunch of Mana and Earth Elementals. This can be a great Primal Earth Farming spot. If you just kill all the Elementals around one of the edges, you can get Primal Earth and Primal Mana at the same time. This makes these farming locations very viable for gold farming.
Nagrand Primal Earth Farming
Nagrand is absolutely riddled with Earth Elementals. The map below might look like a complete mess, but if you just fly around these spots, you will find tons of Earth Elementals. Especially the Elemental Plateau and the southern edge are worth it.