French researchers have determined that the temperature of the Earth’s core is 10,800 degrees Fahrenheit (6,000 oC) – about 1,800 oF (1,000 oC) hotter than previously thought.

The Earth’s core consists mainly of a sphere of liquid iron at temperatures above 7,200 degrees Fahrenheit and pressures of more than 1.3 million atmospheres. Under these conditions, iron is as liquid as the water in the oceans. It is only at the very center of the Earth, where pressure and temperature rise even higher, that the liquid iron solidifies.

To generate an accurate picture of the temperature profile within the Earth’s centre, scientists can look at the melting point of iron at different pressures in the laboratory, using a diamond anvil cell to compress speck-sized samples to pressures of several million atmospheres, and powerful laser beams to heat them to 7,200 or even 9,000 degrees Fahrenheit.

”In practice, many experimental challenges have to be met as the iron sample has to be insulated thermally and also must not be allowed to chemically react with its environment. Even if a sample reaches the extreme temperatures and pressures at the center of the Earth, it will only do so for a matter of seconds. In this short timeframe it is extremely difficult to determine whether it has started to melt or is still solid,” explained Dr Agnès Dewaele of the Commissariat à l’Énergie Atomique, France, co-author of a paper published in the journal Science.

“We have developed a new technique where an intense beam of X-rays from the synchrotron can probe a sample and deduce whether it is solid, liquid or partially molten within as little as a second, using a process known diffraction. This is short enough to keep temperature and pressure constant, and at the same time avoid any chemical reactions,” added Dr Mohamed Mezouar of the European Synchrotron Radiation Facility, France.

The team determined experimentally the melting point of iron up to 8,700 degrees Fahrenheit and 2.2 million atmospheres pressure, and then used an extrapolation method to determine that at 3.3 million atmospheres, the pressure at the border between liquid and solid core, the temperature would be 10,800 degrees Fahrenheit.

“We are of course very satisfied that our experiment validated today’s best theories on heat transfer from the Earth’s core and the generation of the Earth’s magnetic field. I’m hopeful that in the not-so-distant future, we can reproduce in our laboratories, and investigate with synchrotron X-rays, every state of matter inside the Earth,” Dr Dewaele concluded.

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Bibliographic information: S. Anzellini et al. 2013. Melting of Iron at earth’s Inner Core Boundary based on Fast X-ray Diffraction. Science, vol. 340, no. 6131, pp. 464-466; doi: 10.1126/science.1233514