Thermodynamics of iron at extreme pressures and temperatures

• Identifies incompatible data from various studies.
• Provides EOS under core conditions.
• Sets the upper limit on the central core temperature.
• Establishes the heat content of the inner core.
• Emphasizes and quantifies the case for a significant presence of light elements in the inner core.

A thermodynamic database on all iron phases (BCC, FCC, HCP and melt) has been created using thermochemical and equations of state data from experiments and theory. The database permits the calculation of the phase diagram of iron to physical conditions of the Earth's core (pressure of 365 GPa and temperature of 6453 K). If the inner core were all iron, its upper temperature would be 6453 (500) K. The average heat capacity of a pure iron HCP inner core is calculated as 29.4 J/mol/K with an entropy of 92 J/mol/K and a gruneisen parameter of 1.81.