the temperature at which a phase change takes place depends on pressure. For instance because there is more pressure at low altitudes than at high altitudes, water boils at less than 100 degrees Celsius at high altitudes like mount Everest. In general, the higher the pressure, the higher the melting and boiling points are. Therefore potentially the melting point of iron-nickel alloys is significantly greater in the Earth's core than on the Earth's surface due to an enormous pressure within the Eaerth's core.
