Xiaodong Song et al, University of Illinois at Urbana-Champaign suggest in Nature Geoscience that the innermost core of our planet has another region at its centre. The structure of the iron crystals there is different from those found in the outer part of the inner core.
(graphics from BBC Earth)
Song analysed how echoes from earthquakes change as they travel through the different layers of the planet. This suggests that the Earth’s inner core – a solid region that is about the size of the Moon – is made up of two parts.
The core, which lies more than 5,000km down, started to solidify about a billion years ago – and it continues to grow about 0.5mm each year.
The finding that it has crystals with a different alignment, suggests that they formed under different conditions and that our planet may have undergone a dramatic change about half a billion years ago – its magnetic field may have switched between the equatorial axes and the polar axis.
As usual, the artists speculated about this before the scientists found any evidence.