Seismic waves are being used by scientists to investigate the world’s deepest mystery, the Earth’s inner core.
A research team at the University of Illinois and at Nanjing University in China have found that the inner core has an inner core of its own and has surprising properties.
Led by Xiaodong Song, a professor of geology, and postdoctoral researcher Tao Wang, the team published its work in the journal Nature Geoscience.
“Even though the inner core is small – smaller than the moon – it has some really interesting features,” said Song.
“It may tell us about how our planet formed, its history, and other dynamic processes of the Earth. It shapes our understanding of what’s going on deep inside the Earth.”
Researchers use seismic waves from earthquakes to scan below the planet’s surface, like doctors use ultrasound.
Looking through the core revealed a surprise at the centre of the planet, but not that of the other worlds envisioned by novelist Jules Verne who wrote Journey to the Centre of the Earth, a classic science fiction novel, in 1864.
The 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 are aligned north-south. However, in the inner-inner core, the iron crystals point roughly east-west.
Not only are the iron crystals in the inner-inner core aligned differently, they behave differently from the outer-inner core. This means that the inner-inner core could be made of a different type of crystal.
“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 centre – literally, the centre of the Earth.”
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