The atom at the centre of the Earth

Last year it was 150 years since Jules Verne published his Journey to the Centre of the Earth. His basic premise was that some volcanic vents extended all the way from the surface to the Earth’s centre. His not unreasonable plot then made his heroes descend into the Icelandic volcano Snæfellsjökull, encountering many adventures, including prehistoric animals and natural hazards, before eventually coming to the surface again in southern Italy, at the Stromboli volcano”.

But physically reaching the centre of the Earth is probably more distant than even a human colony on a planet around Alpha Centauri. Speculations and models about what the Earth’s core is like is primarily based on the analysis of seismic waves and the manner in which they travel through the various layers making up the Earth’s interior.

A new analysis suggests that the Earth’s inner core has a further inner core. And probably that inner core has another inner core and so on ad infinitum! And even the one atom of Iron, right at the centre of the Earth, itself has an inner core called a nucleus.

Xiaodong Song et al. Equatorial anisotropy in the inner part of Earth’s inner core from autocorrelation of earthquake coda. Nature Geoscience, Feb 9, 2015

Song et al

Press ReleaseThe inner core, once thought to be a solid ball of iron, has some complex structural properties. The team found a distinct inner-inner core, about half the diameter of the whole inner core. The iron crystals in the outer layer of the inner core are aligned directionally, north-south. However, in the inner-inner core, the iron crystals point roughly east-west. (See graphic for a visual map of the inner core.)

Not only are the iron crystals in the inner-inner core aligned differently, they behave differently from their counterparts in the outer-inner core. This means that the inner-inner core could be made of a different type of crystal, or a different phase.

“The fact that we have two regions that are distinctly different may tell us something about how the inner core has been evolving,” Song said. “For example, over the history of the earth, the inner core might have had a very dramatic change in its deformation regime. It might hold the key to how the planet has evolved. We are right in the center – literally, the center of the Earth.”

But this is all still modelling. It looks unlikely that we will be able to design a probe – let alone a vehicle – which can actually reach the centre of the Earth anytime soon. The centre of the Earth lies about 6,000km from the surface. The deepest level accessed physically by humans has been the 3400m that South African gold miners sometimes go down to. The deepest naturally occurring place that can be visited is probably the 2080m to the bottom of the Voronya cave in the Western Caucasus. The deepest oil wells are about 10 km deep. Possibly the deepest hole ever achieved is the Kola bore hole which reached 12,200m.

But who can tell? Maybe Jules Verne’s mysterious volcano tubes will one day be found.

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