The Amulet of Eternity was an artifact previously worn by the High Priest of The Golden Abyss. This amulet represented time before the Earth was made, before Mahuquotex and Chihopotex were separated by Itzicaltli at their sundering of the heavens.
Uncharted: Golden AbyssEdit
This amulet belonged to the grandfather of Marisa Chase. In Uncharted: Golden Abyss, she carried it with her at all times, as it was very special to her. However, Nathan Drake warned her that this artifact was not worth her life, as Roberto Guerro and his men were after that same artifact.
At the end of Golden Abyss, after Nate and Marisa were rescued by Victor Sullivan, she decided that the amulet really wasn't worth it, and tossed it off the ledge of the tall temple were on, never to be seen again.