Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

All change at the Earth's core

20.08.2007
It is hard to know what is going on over 3000 km beneath our feet, but until recently scientists were fairly confident that they understood the way the iron atoms in the Earth’s core packed together. However, new research has overturned conventional thinking and revealed that the structure of the core is not as straightforward as was once thought.

Pressures and temperatures at the Earth’s core are stupendous – more than 3.5 Mbar and 7000K – and currently it is impossible to recreate these conditions in the laboratory. Our information about the core comes from observing the way that seismic waves travel through the core, extrapolating from experimental studies and studying iron rich meteorites.

As a result we know that the core is mostly iron, but that it also must contain some light impurities such as oxygen, silicon, sulphur, hydrogen and magnesium (because the density of the core is too low to be pure iron). The most significant impurity is thought to be nickel, which makes up between 5 and 15% of the composition.

Most studies on the Earth’s core have approximated the composition to be pure iron. “It was assumed that the alloy elements were not very important for the structural and elastic properties of the core,” says Igor Abrikosov, a theoretical physicist at Linköping University in Sweden.

Experimental and theoretical studies on pure iron led to a ‘standard model’ for the core, which said that the iron atoms were packed in a ‘hexagonal close packed’ formation. This resembles a honeycomb structure in which the atoms are in densely packed layers of hexagons, with every other layer lying directly above its partner two layers below.

Other packing structures were ruled out because they were assumed to be less energetically efficient. “At moderate pressures other structures have some magnetism and they turn out to have lower stability,” explains Abrikosov.

Carrying out experiments at anything close to the pressures and temperatures experienced at the core is pretty much impossible. “To achieve high pressures the sample has to be made very small and then it is difficult to see the diffraction patterns from the structures,” explains Leonid Dubrovinsky, a geo-scientist at the University of Bayreuth in Germany. What is more, at high temperatures the iron tends to diffuse and react with the carbon in the diamond anvil cell – a device that pinches samples between two diamond points and creates extreme pressures.

An inability to recreate core conditions hampered our understanding of the core, but in recent years powerful computer models have stepped in the breach. “Expertise has been developed in ‘Ab intio’ (first principles) calculations and we are able to do higher quality extrapolations to understand core conditions,” says Abrikosov.

In addition experiments have improved greatly, with very high pressures and temperatures reached recently in new diamond anvil cells. Combined with the use of synchrotron radiation scientists have been able to observe structures at conditions that are ever closer to conditions at the Earth’s outer core.

Using this combination of theory, experiments and powerful simulations Abrikosov, Dubrovinsky and their colleagues have revisited the core. This time they have also included alloy elements such as Nickel and Magnesium in their calculations and, to their surprise, they found that it has a significant effect.

“At high pressures the magnetism is squeezed out of the other structures and they all have similar stability,” says Abrikosov, who presented his findings at the 1st EuroMinScI Conference near Nice, France in March this year. The new research has revealed that ‘face centred cubic’ and ‘body centred cubic’ structures can not be ruled out and that all of these structures are energetically possible. “The standard model has been killed,” says Abrikosov.

EuroMinScI is the European Collaborative Research (EUROCORES) Programme on “European Mineral Science Initiative” developed by the European Science Foundation (ESF).

Face centred cubic structures have an atom in the centre of every face, as well as at each of the corners, while body centred cubic has one atom in the centre of the cube. Compared to the hexagonal close packed the face centred cubic structure alternates every third layer, with the atoms making a spiral pattern up through the layers.

Elements like nickel, silicon, oxygen and magnesium are also likely to play a key part in way atoms pack in the core. Recent experiments have shown that at very high pressures magnesium atoms are compressed to such an extent that they can fit easily into iron structures. In addition the element nickel is more comfortable than iron in a ‘face centred cubic’ structure.

So why does this matter and what kind of difference could these structures make in the core" “It has implications for the anisotropy of the core,” says Dubrovinsky.

Studies of seismic waves have revealed that the waves travel faster in a north-south direction and slower in an east-west direction through the core – a phenomenon that scientists call anisotropic. The way the atoms pack in the core is vital for understanding this anisotropy.

What is more, the Earth’s core produces our magnetic field. Without it the Earth would be bombarded with dangerous cosmic rays and life would struggle to survive. As well as relying on Earth’s magnetic field to protect us, we now use it to navigate and keep satellites in place. Life on Earth depends upon the magnetic field, but until we understand the core we can’t fully understand how this field is created, or how it is likely to change.

For scientists studying the Earth’s core it is time to go back to the drawing board and rethink what lies underneath our feet. However, a new generation of powerful computer simulations, along with experiments that we could previously only dream about, mean that optimism is high and scientists are confident that the core will reveal its secrets soon.

Sofia Valleley | EurekAlert!
Further information:
http://www.esf.org

More articles from Earth Sciences:

nachricht NASA eyes Pineapple Express soaking California
24.02.2017 | NASA/Goddard Space Flight Center

nachricht 'Quartz' crystals at the Earth's core power its magnetic field
23.02.2017 | Tokyo Institute of Technology

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>