Iron makes up most of the Earth's core, which is very hot and exists under extreme pressures. As such, the physics of iron's behavior under these conditions is of great interest to scientists, because many of the planet's dynamics are determined by it, including the magnetic field that shields the planet's life from deadly cosmic rays.

It is thought that iron reaches its melting point under the conditions found at the so-called Inner Core Boundary, which is found 5,150 kilometers deep. The Inner Core Boundary is where the solid iron of the inner core melts into the liquid iron of the outer core. But there is no consensus on the temperature at which melting occurs.  

Using diamond-anvil cell technology combined with X-ray absorption spectroscopy, a research team led by the Geophysical Laboratory's Reinhard Boehler was able to demonstrate a melting temperature of 3,090 K (about 5,100 degrees Fahrenheit) in the 100-gigapascal pressure range (about a million times normal atmospheric pressure).

Their work was published in PNAS.

                                        

Caption: (A) Schematics of the sample loading. (B) Sample containment using single-crystal sapphire. (Left) Disk before loading. The disk is 10 μm thick, with a cavity 18μm in diameter and 6μm deep machined with FIBM. The iron sample with the same dimensions is laser-cut from a foil. (Center) Picture in transmitted light taken at 24 GPa before heating. The capsule shows no sign of cracks. (Right) Picture taken at 100 GPa after three heating/melting events.

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