Linking the Inner and Outer Core: Another Piece in the Jigsaw of Understanding the Deep Earth

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Differential rotation fo the inner and outer cores. Image credit: Phil Livermore

Differential rotation of the inner and outer cores. Image courtesy of: Dr. Phil Livermore

New research published this week shows a link between the motions of two parts of the Earth’s core, spinning at different speeds and in different directions.

A random bit of scientific research, only interesting to a select group of geoscientists, you might think… Well, no. The Earth’s core functions as a giant magnet, and generates the planet’s magnetic field – and that’s why research into the Earth’s core is potentially relevant to us all.

The Earth’s Geomagnetic Field

The centre of the Earth has never been sampled, but geophysical techniques have revealed that it’s composed of an inner core, made of solid iron, and an outer core which is made of a metal alloy – and which is liquid.

Electric currents generated within the core turn it, in effect, into a giant magnet and are the main source of the planet’s magnetic field (there are other, terrestrial and extra-terrestrial influences and anomalies).

Over 300 years ago the Astronomer Royal, Edmund Halley, noticed that observations of the declination (the difference between true north and magnetic north) had changed. Subsequent observations have confirmed a continued ‘westwards drift.’

More recently, seismic observations based upon records from near-identical earthquakes occurring at different times in the same location have indicated that the rotational speed and direction of the inner core differ from those of the outer core. The former spins eastwards, relatively quickly (faster than the Earth as a whole) while the latter spins westwards at a relatively slower rate.

Sampling the Earth’s Core

The Earth's core operates as a giant magnet. Image credit: Zureks

The Earth’s core operates as a giant magnet. Image credit: Zureks

It’s obviously impossible for scientists to sample the Earth’ score directly. In this case, researchers from the University of Leeds and the Swiss Federal Institute of Technology in Zurich used a complex computer model to try and establish a link between the relative movements of the core and the observed westward drift.

Leeds University’s Dr Philip Livermore tells Decoded Science, “the most important aspect [is] the linkage between the recently discovered superrotation of the inner core and the westward drift in the outer core… these two features are observed using completely independent techniques, and it is far from clear that they are linked.

Earth’s Magnetic Core: Relevance of the Research

So why is it important for us, on the surface of the planet? The Earth’s magnetic field has an impact on us all and if many aspects have been little understood until now, then this research is part of changing all that.

A better understanding of the generation process would undoubtedly help us predict the future of the structure of the magnetic field (our magnetic shield),” Dr Livermore told Decoded Science. “In a similar way, how aurorae and geomagnetic storms might behave in the future could in principle be predicted if we had the tools to do so.

Magnetic storms, such as this in 2003, can cause extensive damage to communications. Image credit: US Government

Magnetic storms, such as this in 2003, can cause extensive damage to communications. Image credit: US Government

Links between the magnetic field of the earth and the planet’s core (which we don’t see) and the environment around us (by which we are very strongly and directly affected) do exist, and are of direct relevance to us – even though we don’t fully understand them yet.

For example, the field protects us from perturbations in the sun’s radiative activity – and such ‘space weather’ is, as Dr Livermore points out, a new addition to the UK’s National Risk Register for Civil emergencies – which explains that such disturbances “could have impacts upon a range of technologies and infrastructure, including power networks, satellite services, transport and digital control components” – potentially a serious problem in an increasingly digital age.

What about other impacts? If earthquakes can be used as ‘tracers’ of the different movements between the two parts of the core, can they be affected by it? On this, Dr Livermore is more sceptical: “I don’t know of any robust physical mechanism that links seismic activity and geomagnetism, although this view is not shared by everyone,” he says. In fact, he points out, we simply don’t know enough about the structure of the Earth.

We Don’t Know Enough About Earth

But that may be changing. “Understanding the generation of Earth’s magnetic field is in many ways a little like doing a jigsaw. We are aware of many of the pieces, but just not how they all fit together – every new link helps the whole process move forward,” says Dr Livermore.

It’s taken scientists three centuries to solve the riddle of westward drift of the geomagnetic field but our knowledge of the planet continues to grow, and more answers emerge.

Sources:

British Geological Survey. The Earth’s magnetic field: an overview. Accessed 19 September 2013.

P.W. Livermore, R. Hollerbach and A. Jackson. Electromagnetically driven westward drift and inner-core superrotation in Earth’s core. (2013). Proceedings of the National Academy of Sciences. Accessed 19 September 2013.

UK Government. National risk register of civil emergencies 2013 edition. Accessed 19 September 2013.

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