According to scientists studying seismic waves, the Earth’s inner core has a secret. The inner core has its own inner-inner core.
Using earthquake-reading technology, a research team at the University of Illinois and Nanjing University in China have found that the inner-inner core of the planet has some surprising qualities which could enhance our understanding of our planet’s history and how it works.
The Earth is made up of three major layers. The solid outer crust, where we live, contains all known life. Beneath that is a hot layer of magma, semi-solid rocks and minerals called the mantle. It is the movement of the mantle that causes tectonic activity such as earthquakes and volcanic eruptions.
Beneath the mantle is the core, and the inner core. a 1400 mile, constantly spinning ball of super-heated metal. Because the ball is made of metal, it makes the entire planet magnetic. This is what creates the Earth’s magnetic field, protecting us from cosmic radiation.
“Even though the inner core is small – smaller than the moon – it has some really interesting features. 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,” Xiaodong Song, a professor of geology at the U. of I. in a statement.
The researchers used seismic waves generated by earthquakes to scan below the planets surface. The technology is similar to the ultrasound technology used by doctors to look inside patients.
The team used data gathered from the waves that resonate following the initial shock of an earthquake. They describe this a being “like a hammer striking a bell, much like a listener hears the clear tone that resonates after the bell strike, seismic sensors collect a coherent signal in the earthquake’s coda.”
“It turns out the coherent signal enhanced by the technology is clearer than the ring itself. The basic idea of the method has been around for a while, and people have used it for other kinds of studies near the surface. But we are looking all the way through the center of the Earth,” said Song.
According to the research, published in the February 9 edition of the the journal Nature Geoscience, the inner core has some interesting and unexpected properties. Once thought to be entirely made of iron, it showed unusual structural properties.
The inner-inner core, about half the diameter of the whole inner core, contained iron crystals with a different orientation than the outer-inner core. The crystals in the outer layer were aligned north-south, but the inner-inner core had crystals pointing east-west.
The team also found that the iron crystals in the inner-inner core behave differently than the crystals in the outer-inner core. This could mean that they are a different type of crystal or the crystals are in 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. 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,” said Song.
According to Professor Simon Redfern from the University of Cambridge, the discovery could reveal secrets about the Earth’s history and explain some ancient mysteries.
“If this is true, it would imply that something very substantial happened to flip the orientation of the core to turn the alignment of crystals in the inner core north-south as is seen today in its outer parts,” Redfern told the BBC.
“It could be that the strange alignment Prof Song sees in the innermost core explains the strange palaeomagnetic signatures from ancient rocks that may have been present near the equator half a billion years ago,” Redfern added.
The discovery could help scientists understand the Earth better. It could also help researchers to gain a better understanding of other planets.
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