Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists probe link between magnetic polarity reversal and mantle processes

31.07.2012
Scientists at the University of Liverpool have discovered that variations in the long-term reversal rate of the Earth's magnetic field may be caused by changes in heat flow from the Earth's core into the base of the overlying mantle.

The Earth is made up of a solid inner core, surrounded by a liquid outer core, in turn covered by a thicker or more viscous mantle, and ultimately by the solid crust beneath our feet.

The magnetic field is generated by the motions of the liquid iron alloy in the outer core, approximately 3,000 km beneath the Earth's crust. These motions occur because the core is losing heat to the overlying solid mantle that extends up to the crust on which we live.

The mantle itself is also in motion but at much slower speeds of millimetres per year as opposed to millimetres per second in the core. This mantle motion is responsible for the drifting of the continents at the surface as well as earthquakes, volcanoes, and changes in the climate over millions of years.

At intervals of hundreds of thousands of years, the North and South magnetic poles reverse and scientists can tell from rock formations precisely at what periods in the past this took place. The most recent reversal happened 780,000 years ago. Magnetic field variations happen on timescales of months to millions of years. Much of the magnetic field's variation is thought to be sporadic but new research, led by Liverpool scientists, has found that over long timescales, this variability may be related to the changing pattern of heat loss across the core-mantle boundary occurring over millions of years.

The team performed a detailed synthesis based on latest findings from a number of different areas including the ancient geomagnetic field and its record in rocks, motions in the mantle caused by motions of the continents and the process responsible for generating the magnetic field in the core.

Dr Andrew Biggin, from the University's School of Environmental Sciences, said: "The magnetic field has undergone big changes in its behaviour that might be due to the mantle's controlling influence on the core. In particular, we focused on the time interval between around 200 and 80 million years ago – when dinosaurs were still around – when the magnetic field initially started reversing its polarity very frequently. During this period the polarity was reversing up to 10 times every million years; however 50 million years later, it stopped reversing altogether for nearly 40 million years.

"When these changes in the magnetic field were taking place, the whole of the Earth's crust and mantle, including all of the continents, were undergoing a big rotation with respect to the geographic and time-averaged geomagnetic poles – the points defining the Earth's axis of rotation. We suspect that this process, called True Polar Wander and caused by the changing density distribution in the mantle, will have changed the pattern of heat flowing out of the core in such a manner as to cause the magnetic field to first become less stable, with lots of reversals, and then become much more stable – and stop reversing."

The team believes this may not be the only explanation and conjecture that this big drop in the frequency of reversals may also be related to a similar decrease in the number of 'large igneous provinces' (LIPs) or concentrated outpourings of magma from the Earth's core, 50 million years later. The last LIP happened around 16 million years ago and produced the Columbia Plateau in the North West US. LIPs are thought to be produced by hot plumes of material rising from thermal instabilities near the bottom boundary of the mantle.

The team believes the 50 million year time lag between the magnetic field changing and the occurrence of the LIPs could represent the time it takes for the plumes to travel 2,890 km through the mantle. If this link were correct it would mean that the rather unstable magnetic field observed in the last 50 million years predicts that a considerable number of LIPs will erupt over the next 50 million years. This in turn could have major implications for the surface conditions – for climate and for life itself.

The research, published in Nature Geoscience, is a collaboration between the University of Liverpool, GFZ Potsdam, IPGP Paris, the University of Oslo and Utrecht University. Future research at Liverpool, is planned and already underway to develop a new tool for understanding the Earth's system.

Kate Mizen | EurekAlert!
Further information:
http://www.liv.ac.uk

More articles from Earth Sciences:

nachricht Climate Change in West Africa
17.06.2019 | Julius-Maximilians-Universität Würzburg

nachricht Determining the Earth’s gravity field more accurately than ever before
13.06.2019 | Technische Universität Graz

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Successfully Tested in Praxis: Bidirectional Sensor Technology Optimizes Laser Material Deposition

The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.

Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...

Im Focus: The hidden structure of the periodic system

The well-known representation of chemical elements is just one example of how objects can be arranged and classified

The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...

Im Focus: MPSD team discovers light-induced ferroelectricity in strontium titanate

Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.

Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...

Im Focus: Determining the Earth’s gravity field more accurately than ever before

Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.

The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...

Im Focus: Tube anemone has the largest animal mitochondrial genome ever sequenced

Discovery by Brazilian and US researchers could change the classification of two species, which appear more akin to jellyfish than was thought.

The tube anemone Isarachnanthus nocturnus is only 15 cm long but has the largest mitochondrial genome of any animal sequenced to date, with 80,923 base pairs....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

 
Latest News

A new force for optical tweezers awakens

19.06.2019 | Physics and Astronomy

New AI system manages road infrastructure via Google Street View

19.06.2019 | Information Technology

A new manufacturing process for aluminum alloys

19.06.2019 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>