Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. Earth Science News .




TECTONICS
Magnetic field, mantle convection and tectonics
by Staff Writers
Munich, Germany (SPX) Aug 02, 2012


It is known that the Earth's magnetic field is produced by convection currents of an electrically conducting iron-nickel alloyin the liquid core, about 3,000 kilometers below the earth's surface. The geomagnetic field is highly variable, there are changes in Earth's magnetic field on a multitude of spatial and temporal scales.

On a time scale of tens to hundreds of millions of years, the geomagnetic field may be influenced by currents in the mantle. The frequent polarity reversals of Earth's magnetic field can also be connected with processes in the mantle.

These are the research results presented by a group of geoscientists in the new advance edition of "Nature Geoscience" on Sunday, July 29th. The results show how the rapid processes in the outer core, which flows at rates of up to about one millimeter per second, are coupled with the processes in the mantle, which occur more in the velocity range of centimeters per year.

The international group of scientists led by A. Biggin of the University of Liverpool included members of the GFZ German Research Centre for Geosciences, the IPGP Paris, the universities of Oslo and Utrecht, and other partners.

It is known that the Earth's magnetic field is produced by convection currents of an electrically conducting iron-nickel alloyin the liquid core, about 3,000 kilometers below the earth's surface. The geomagnetic field is highly variable, there are changes in Earth's magnetic field on a multitude of spatial and temporal scales.

Above the liquid outer core is the mantle, the rock in which behaves plastically deformable due to the intense heat and high pressure. At the boundary between Earth's core and mantle at 2900 km depth there is an intense heat exchange, which is on the one hand directed from the Earth's core into the mantle.

On the other hand, processes within Earth's mantle in turn also affect the heat flow. The interesting question is how the much slower flow in the solid mantle influences the heat flow and its spatial distribution at the core-mantle boundary, and how this will affect the Earth's magnetic field which is produced due to the much faster currents in the Earth's core.

Key variable heat transfer
"The key variable is the heat flow. A cooler mantle accelerates the flow of heat from the hot core of the Earth, and in this way alters the also heat-driven convection in the Earth's core", said Bernhard Steinberger of the GFZ German Research Centre for Geosciences.

"Ocean floor sinking into the mantle due to tectonic processes can lead to cooling in the mantle. They cause at these sites an increased heat flow into the cooler parts, namely until they have been heated to the ambient temperature." That might take several hundred million years, however.

Conversely, the hot core of the Earth leads to the ascent of heated rocks in form of large bubbles, so-called mantle plumes that separate from the core-mantle boundary and make their way up to the surface of the earth. This is how Hawaii came into existence. This increases the local heat flux out of the earth's core and in turn modifies the generator of the geomagnetic field.

Reversals of the magnetic field
In the Earth's history, polarity reversals of the geomagnetic field are nothing extraordinary. The most recent took place only 780 000 years ago, geologically speaking a very short period of time.

The research team was able to determine that in the period of 200 to 80 million years before present, reversals initially happened more often, namely up to ten times in hundred million years. "Surprisingly, these reversals stopped about 120 million years ago and were absent for nearly 40 million years," explains GFZ scientist Sachs.

Scientists presume that the reason for this is a concurrent reorientation of the whole mantle and crust with a shift in the geographic and magnetic poles of about 30 degrees.

Known as "true polar wander", thisprocess is caused by a change in density distribution in the mantle. If it increases the heat flux in equatorial regions, it would presumably lead to more frequent field reversals, if it decreases it, the field reversal might not occur.

Looking to the future
According to current knowledge, therefore, an influence of plate tectonics and mantle convection on the Earth's magnetic field seems quite possible.

The article also shows, however, that further research is still needed for a better understanding of these relationships. In particular, more episodes of "true polar wander" should be derived from paleomagnetic data, and it should be determined whether these are usually associated with an altered behavior of the magnetic field (e.g. frequency of field reversal).

Also, future models for the generation of the geomagnetic field should investigate the influence of the spatial and temporal variation of the heat flux at the core-mantle boundary in more detail.

J. Biggin et al., "Possible links between long-term geomagnetic variations and whole-mantle convection processes", Nature Geoscience, Vol. 5, August 2012, doi:10.1038/NGEO1521

.


Related Links
Helmholtz Association of German Research Centres
Tectonic Science and News






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TECTONICS
Alpine faults show new evidence for regular magnitude 8 earthquakes
Reno NV (SPX) Jul 31, 2012
A new study published in the prestigious journal Science, co-authored by University of Nevada, Reno's Glenn Biasi and colleagues at GNS Science in New Zealand, finds that very large earthquakes have been occurring relatively regularly on the Alpine Fault along the southwest coastline of New Zealand for at least 8,000 years. The Alpine Fault is the most hazardous fault on the South Island o ... read more


TECTONICS
Queen, politicians, Nobel winner named to UN social panel

Sri Lanka navy urges Australia to deport boatpeople

Samurai festival returns to disaster-hit Japan

UNHCR official to visit Rakhine state

TECTONICS
From Microns to Centimeters

Raytheon awarded contract to advance Dual Band Radar development

Apple extends gains in surging tablet market: survey

Apple asks for verdict after Samsung 'misconduct'

TECTONICS
France's Veolia boosts cost cutting, stock tumbles

Earth absorbs more of our CO2 emissions: science

Spillways can divert sand from river to rebuild wetlands

Coral reef thriving in sediment-laden waters

TECTONICS
Researchers analyze melting glaciers and water resources in Central Asia

Who owns the North Pole?

China to build first polar-expedition icebreaker

Hidden rift valley discovered beneath West Antarctica reveals new insight into ice loss

TECTONICS
UCLA research makes possible rapid assessment of plant drought tolerance

Parched fields as drought devastates US crops

Public strongly supports programs helping farmers adapt to climate change

Study: All chickens have Asian roots

TECTONICS
Six dead as Typhoon Saola lashes Taiwan

N. Koreans urgently need drinking water after floods: UN

Philippine floods persist, toll rises to 23

Typhoon Saola makes landfall in Taiwan

TECTONICS
Mali wives prevent loyalist soldiers' arrest

Panetta to visit North Africa, Middle East

Brother of exiled Rwandan ex-army chief gets 9 years' jail

Mozambique told to tackle crime

TECTONICS
Modern culture 44,000 years ago

Hey, I'm over here: Men and women see things differently

Piglets in mazes provide insights into human cognitive development

Genomic study of Africa's hunter-gatherers elucidates human variation and ancient interbreeding




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement