A new study suggests that the differences between the east and west hemispheres of the Earth’s core are explained by the way iron atoms pack together.
Lying more than 5,000km beneath our feet, at the centre of the Earth, the core is beyond the reach of direct investigation.
Broadly speaking, it consists of a solid sphere of metal sitting within a liquid outer core.
The inner core started to solidify more than a billion years ago. It has a radius of about 1,220km, but is growing by about 0.5mm each year, the BBC reported.
But the stuff that the core is made from remains a longstanding unresolved problem.
Clues come from the speeds that seismic waves generated by earthquakes pass through the core.
These tell us its density and elasticity, but the precise arrangement of iron atoms forming the crystalline core controls these numbers.
How those atoms are arranged remains unclear, since the conditions of extreme pressure and temperature at the core cannot easily be replicated in the laboratory.
Seismic data indicate that the western and eastern hemispheres of Earth’s inner core differ, and this has led some to suggest that the core was once subjected to an impulse - presumably from the collision of a space rock or planetoid which shook the whole Earth.
The core, it is suggested, is constantly moving sideways. As it does, the front side is melting and the rear side crystallising, but the core is held centrally by gravity.
With all these seismic complexities, the link between the crystal structure and the geophysical observations has yet to be resolved.
The study is published in the journal Scientific Reports.