Earth Magic is usually defensive, through the use of wards.
For a PvE Prophecies Earth Magic build I'd go for something like:
[skill]Earth Attunement[/skill][skill]Glyph of Lesser Energy[/skill][skill]Eruption[/skill][skill]Earthquake[/skill][skill]Enervating Charge[/skill][skill]Stoning[/skill][skill]Ward Against Melee[/skill][skill]Resurrection Chant[/skill]
When you can, I'd use [wiki]Elemental Attunement[/wiki]. Earth skills tend not to be that spammable, so you could include Stoning in there if you feel there are times when you're not doing much. Alternatively you could use [wiki]Glyph of Renewal[/wiki] to allow you to use Eruption more, or [wiki]Glyph of Energy[/wiki] to allow you to spam Earthquake more.
An Earth Ele should always have at least one ward in my opinion. You can switch it for whatever is most useful. For instance, int he Southern Shiverpeaks I suggest you consider [wiki]Ward against Elements[/wiki] or [wiki]Ward of Stability[/wiki], since the Stone Summit Herder's knockdowns can be very irritating.
You don't need many Attribute Points in Air, Enervating Charge is just for the Weakness so that Stoning knocks down.