Earth's Magnetic Field

They do, but very weakly.

Hitting the material can help. Hands up, I don't totally understand that and had to look on Google. One article caught my eye, though it's slightly base over apex. It uses big words, so it must be good .

Magnetism is one of those everyday things that (for me) still resides on the voodoo shelf. We can observe it's effects, but I suspect that physicists are not entirely in agreement about it (?).

In my studies of the magnetic properties of materials (and it's a long story how I got there from an academic study of mineralogy and a tool maker trade), one of the best reference books I used made the statement (to paraphrase) If we were unaware of the Iron group of elements (Fe, Ni, Co) our current theories about the magnetic properties of materials could not predict the phenomenon of Feromagnitisim.

Yes there is some Voodoo there. But then that was 30 years ago.

I didn't express myself too well (and will probably manage it again). As with yourself, my academic background is in rock. I'll defer to you since all I know is rock mehanics, and magnestism is not much more than background info in that area. I was clumsily trying to get at how particle phusicists regard the topic of magnetism.

Rixter : You may have been refering to the mid-atlantic ridge. That's a divergent zone in which material spews upward and spreads out on either side. All that nice fresh rock takes on the polarity existing at the time. The marianas is a subduction zone (one plate slipping under another) - the plate that dives gets melted, and it interacts with the upper one to cause orogony (mountain building and seismic activity), all those mountains along the spine of the Americas are there for a reason that very reason. There's doubtless magnetization in the diving plate of the Marianas (which is in the Pacific), but it's not the classic case for plate tectonics cited in text books. That being a subduction zone is also a big factor in mineralization of said mountains. The mid-atlantic also gets cited for another reason - the west coasts of Europe/Africa has more than a passing resemblance to the east coast of the Americas.The Appalacians have been tracked all the way from America to Scotland and down thru Europe. Bit of a gap inbetwixt, but the geology fits (there are other reasons for tying the two together). Haven't checked it recently, but there is a project to create a walking route called the Appalacian Way (just a guess, but folk need to do one leg of the journey over water ).

Blyth and de Freitas is a reasonable read for engineering/geology though it's neither one or the other. Jaeger and Cooks tome is, even though dated, a real brain acher.

Just an aside, but the earths magnetic feild is far from being a nice bar magnet type thing. It's a bistable system, that looks incredibly unstable as it moves toward a flip.

For anybody in need of a headache....

And that is why naval ships and submarines will go through a de-gaussing process to clear the hull of its magnetic signature that develops as a result of its travels through the lines of flux.

All and I mean ALL the ships I served on had degaussing cables "built in" so that the process was really easy to do....

I am sure that even today such cables are installed as normal business so to say for at least military ships..Wiki supports this....

This is used to Deperm subs..

Nah, quadrapoles with an occasional octopole thrown in for good measure.

Jesus H. Christ on a Crutch, mate! Magnetic fields ALL come in dipoles, minimum! You might as well exclaim "One plus one equals TWO!!!" for bog's sake.

Where are we? In Chapter Six of "The Marching Morons"?

"One plus one equals TWO!!!" EUREKA...I got to that answer in my calc as well...OMG

Is anyone here connected with the Nobel committee? I think I can prove it from first principles...

Certain Iron rich minerals do become magnetized by the Earth's magnetic field when they crystallize from their parent magma. Although the effect is week, it is measurable especially in Mafic (Mg,Fe silicates) rocks like basalt.

It was observation of this effect that led to the discovery of the periodic reversals of Earth's magnetic field, and sea floor spreading. This was one of the breakthrough proofs of plate tectonic theory.

Some materials are a lot like people...they're lazy and don't follow the magnetic crowd (metaphor galore)!

They do, but the earth's magnetic field is fairly weak, so that anything that gets magnetized by the earth's field is not a very strong magnet.

One example is magnetic minerals retrieved from the San Marianas trench in the middle of the Atlantic Ocean. The direction and strength of magnetization, like a huge tape recorder, has made a record of the earth's field in the past.

http://pubs.usgs.gov/gip/dynamic/understanding.html

"--------- but the earth's magnetic field is fairly weak--------"

So weak as to induce high voltages in space based tether experiments.

So weak as to protect our biosphere from the ionizing radiation of the sun; and the kinetic stripping of our atmosphere.

So weak as to have served as directional reference and reaction field for satellite attitude determination and control --- in the 1960's.

What can Mar's tell us about the future of our own magnetosphere?

Could it be that Mar's is on a Thermodynamic Fast-track in comparison to Earth?

Perhaps as a result of its surface area being much larger per unit volume than Earth; resulting in a significantly higher thermo-entropic rate, and narrowing the thermodynamic window in which a magnetosphere can exist. A geological span of time where the thermal phase states of constituent mass combine with rotational energy to generate a protecting magnetosphere. That window in time when the planetary surface is shielded against the ionizing radiation of the sun and protected from a kinetic stripping of the atmosphere by those same particles.

Mars

fify

So, the general consensus seems to be that the Earth's Magnetic field being significantly weak, it is able to develop very negligible magnetization. In that case, can some one please provide with values of magetic field intensity at different points on the earth's sphere.

Great link! Thanks for finding it. I'd really love to see the same charts updated to this decade.

It would be interesting to see how much it has changed.

Depending on how much time your bar magnets spend under the electric blanket, you'll find the background ac field about the same size as the earth's field, so things get degaussed. Besides, things that magnetize easily usually have a low retentivity and, so, lose their magnetism quickly. Things that require a large field to magnetize usually make better permanent magnets.

It does. The ancient Chinese used Lodestone as a compass.

http://en.wikipedia.org/wiki/Lodestone

Jim

As did the Vikings

This is a copy and paste from an earlier thread related to "Earth's Magnetic Field."

Perhaps the Geo-dynamo is called a dynamo for a reason?

Can the earth be modeled as a spherical shaped dynamo?

Electro-magnetic induction requires three components - a conductor, (it matters not whether the conductor is ferromagnetic), an EXCITATION FIELD, and the Rate of Change.

What is the source of the excitation field? Sol field? Self-excitation as a result of Ionic Charge? What?

What is the source of the Rate Of Change component?

Does the difference between the angular velocity of the core and mantel (Spin Gradient) oscillate from a negative to positive value?

When we consider the difference in rotational energies between a solid inner core, with a liquid interface (outer core) and a highly viscous semi-solid mantle; it can be imagined that high friction convective coupling would occur between the solid inner core and the mantle through that interface.

Would the viscosity of that liquid interface define the rate at which the different rotational energies are translated between the solid core and mantle?

(Let us define Specific Rotational Energy as the rotational kinetic energy per unit mass.)

When you look at the different equations for the moment of inertia of a solid sphere and that of a spherical shell; it becomes obvious that the specific rotation energy would be considerable higher for the mantle than the core. This is based not only on the Constant Ratio given in the equations; but also the square relationship of the moment of inertia to radius.

Let us consider whether it would be possible for the core and mantle to be translating kinetic energy between one and the other. In this consideration let us give the present epoch spin gradient a positive value; that being where the angular velocity of the core is greater than that of the mantle; thereby setting up a magnetic polarization that we will call negative.

As the energy is transferred from the core to the mantle through viscous friction the spin gradient decreases and the magnetic field begins to collapse; converting the magnetic field energy to thermal energy through the process of self-induction and resistive heating; perhaps more so in the liquid interface, thus reducing the viscosity of that liquid interface.

As the spin gradient between core and mantle approaches zero the specific inertial energy of the mantle would cause its rotational velocity to begin to exceed that of the core; thus changing the vector of the spin gradient and reversing the magnetic polarity of the dynamo.(Lentz's Law?)

In this new epoch some of the rotational energy of the core and mantle would again be converted to magnetic energy stored in the earth's magnetic field; somewhat cooling the liquid interface and increasing the coefficient of viscous friction of that interface.

The hypothetical oscillating processes as described above would not only translate to periods of varying geologic activity; but also magnetic field reversals.

Perhaps the Earth, like Mars in the past, will eventually cool with the liquid interface phasing to a solid state, eliminating the Rate of Change Component, and thus ending the dynamo process, eliminating the magnetic field that prevents our atmosphere from being exposed to the ionizing radiation and kinetic energy of the solar wind, resulting in the atmosphere being stripped away.

What percentage of the Earth's magnetic field is due to the electric current from the Sun, ie 'solar wind'/ particle stream etc, in which it is rotating?