Seismic studies tell us about some of the physical properties of Earth’s interior – for example, the density and pressure of the core. However, the associated temperatures cannot directly be calculated and so there has been no consensus, due to the uncertainties involved. Recently in Science, a team of scientists reported the results of new high pressure diamond anvil experiments which measured the melting behaviour of iron under high temperatures and pressures.
The Earth’s core is split into two segments – a solid inner core and a molten liquid outer core, both predominantly made of iron. Therefore the temperature of the inner core/outer core boundary will reflect the melting point of iron metal (or an iron alloy), however the behaviour of iron under the high core pressures (upto 330 GPa or 3.3 million atmospheres) is not well known.
The new experiments involve heating samples of iron contained within a diamond anvil cell by a laser, and analysing the structure of the sample using X-Ray Diffraction. As the samples are heated to different temperatures, the melting point of iron can be determined at high pressures (upto 200 GPa).
These data are subsequently used to build up a temperature profile within the core, suggesting that the Earth’s core temperature is that of the Sun’s surface temperature – around 6000 °C. These results also suggest that there should be a high heat flux out of the core, which may be enough to cause partial melting of the lower mantle. These findings also have implications about the heat budget, the thermal evolution and the maintenance of the Earth’s magnetic field.
