It is obtained through:
- Battles and Level Taxes on most of the Grasslands
- Supply Station
- Tavern (high probability if you opt out of the gold and ham)
- Daily Login Reward (random)
- Online Reward
- Prison (at random when you capture a prisoner)
- Daily Grind Rewards
It can be Synthesized into Pure Earth Essence at the Forge. You need to level up a magic skill of any kind to level 31 before you're able to do this. After all your magic skills are at level 31 or more, this is the only use left for this item.
The max stack of Earth Essences is 9999.