JEB
Legend
Knowledge and Grave domains feel like quite a stretch to work with a primordial, earth elemental theme, looking at their Channel Divinity features. Forge and Nature sound closer but still don't feel "primordial" even reskinned. I suppose you could default to using the war cleric for an earth cleric, but that's because "fights good" is pretty portable - and there's still nothing about it that says "this character draws power from elemental earth".Earth? War, Knowledge, Forge (now), Nature, Grave (now)...
This really isn't hard.
That said, riffing off of @humble minion's point, encouraging PC clerics to customize their domain spell list could help with reflavoring. Provided you then choose something generic like life or war, where the mechanics are more easily disassociated from descriptions.