The Plane of Earth breathes life into the world in the form of the mountains, valleys and plants which they give home to. The Keeper of Earth has long watched over the Plane, keeping the balance of the planets and moons in check by refining the soil for plants to thrive on. Without the Plane of Earth, the planets would be barren rocks, impossible for life to exist. 

Since you have chosen the path of the hero, you must explore the Plane of Earth in search of Earth Signets to take back to the material world. The signets can summon Earth Elemental Relics from the Planes through the Earth Elemental Chest at the Elder Stones.