When the Obelisk was shattered by the Guardian, the Heart of Earth landed in Stone Cove, where Lithos found it and stored it safely in the Catacombs, specifically the Pit of Death part that housed the Chapel of the Dead. It was there, where the Avatar found it in an ancient grave in Ultima VIII, and later used it to drain Lithos of his powers, destroying him in the process. It melted into the other fragments, reforming the Obelisk.