Hotter than the surface of the Sun
Using a delicious combination of particle accelerators, X-rays, high-intensity lasers, diamonds, and iron atoms, scientists have worked out that the inner core of the Earth is actually 6,000 degrees Celsius — some 1,000 degrees hotter than the previous scientific estimate. This means the core of our Earth is actually hotter than the surface of the Sun. This new data could generate repercussions in the fields of geophysics, seismology, geodynamics, and other Earth-oriented scientific disciplines.
From the outside in, the Earth consists of the crust (which are all standing on), the upper mantle (solid), the mantle (mostly solid), the outer core (molten iron-nickel), and the inner core (solid iron-nickel). The outer core is molten due to very high temperatures, but the increased pressure at the center of the Earth means that the inner core remains solid. The distance to the center of the Earth is 6,371 kilometers (3,958 mi), the crust is 35 kilometers (21 mi) thick, the mantle is 2855km (1774 mi) thick — and get this: the deepest we have ever drilled is the Kola Superdeep Borehole, which is just 12km deep. In truth, we have almost no direct knowledge of anything beneath the crust — all of our data is inferred from the seismic waves of earthquakes bouncing off the various layers, and from various bits of the Earth’s interior that bubble up to the surface, such as volcanic magma.
While we would love to dig down to the core and take some exact measurements, it simply isn’t possible with our current drilling technology — and probably never will be. The Kola Superdeep Borehole had to stop at 12 kilometers because the temperature had already reached 180 Celsius (356F), and was expected to reach 300C at the target depth of 15km — at which point, the drill bit would cease to work. There are no drilling technologies that would even come close to surviving in the mantle, which ranges from 500C to 4000C (plus, there’s no oil beyond the crust, so there’s no need to develop such technology…)
To work out the temperature of the inner core, then, the French researchers have essentially done their best to recreate the ultra-high temperature and pressure of the core… in their very-well-equipped laboratory. The hardest bit is recreating the intense pressure of the inner core, which is estimated to be 330 gigapascals (GPa) — more than three million times normal atmospheric pressure. To do this, they use a diamond anvil cell — essentially a diamond-tipped vice (pictured below) — to crush a tiny sample of iron with 200 gigapascals. The iron is then heated with a laser, and then subjected to X-ray diffraction analysis to see how the iron shifts from solid to liquid under these extreme conditions. Finally, the scientists extrapolate their data from 200 GPa to 330 GPa, giving a final estimate of 6230 ± 500 Kelvin (5957 ± 500C, 10755 ± 932F) at the inner core boundary. The temperature at the actual core of the inner core — the center of the Earth — is probably even hotter.
Why is a revised temperature of the Earth’s core important? Well, the simple answer is that the Earth’s magnetic field is generated by the core, and a lot of what happens here on the surface of the Earth is affected by the magnetic field — for one, it prevents our atmosphere from being blown away by the solar wind. Finding out that the Earth’s inner core is actually 1000 degrees hotter than expected won’t have any immediate repercussions, but that’s just how science goes. The updated temperature will be fed into the computer models of seismologists and geophysicists, and who knows: Maybe it will eventually lead to some kind of planetary science breakthrough. In general, the better we understand the world around us, the better our lives will be.
By Sebastian Anthony | ExtremeTech
Research paper: DOI: 10.1126/science.1233514 – “Melting of Iron at Earth’s Inner Core Boundary Based on Fast X-ray Diffraction”