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Offline AndroidNeox

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What causes Earth's magnetic field?
« on: 28/07/2016 09:05:21 »
I've heard that spinning or flowing iron in the Earth's core causes the magnetic field. What is the physical process? Spinning iron doesn't generally cause a magnetic field. Molten iron doesn't have a net field, usually.


 

Offline evan_au

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Re: What causes Earth's magnetic field?
« Reply #1 on: 28/07/2016 09:21:37 »
It is related to electrical current, heat flow and physical movement.

It has been simulated in the laboratory (including the chaotic pole flips).

See: https://en.wikipedia.org/wiki/Earth%27s_magnetic_field#Physical_origin
 

Offline puppypower

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Re: What causes Earth's magnetic field?
« Reply #2 on: 28/07/2016 12:01:45 »
One practical problem is if you heat iron magnets to about 1050C, they will lose their ability to be magnetic.

Quote
A piece of iron ordinarily will be attracted to a magnet, but when you heat the iron to a high enough temperature (called the Curie point), it loses its ability to be magnetized. Heat energy scrambles the iron atoms so they can’t line up and create a magnetic field.

The iron core of the earth exists at a temperature; 6000K, where iron should be a super heated gas. The boiling point of iron is 2860C.

What makes the difference is pressure, which allows iron to become solid phase, at the 6000K and about 3.6 million atmospheres of pressure in the core of the earth. I am not sure, if much work has been done with metallic iron under such extreme conditions to see if the electrons are in higher energy levels, than used for magnetism. My guess is this phase of iron has electrons of very high energy and that currents of electricity form and flow within solid iron continuum. The currents generate magnetic fields. 

There is one additional wild card, which is water. Water at the conditions of the earth's core has been shown in the lab to exist as a metallic solid.

Quote
Water is well known for its astonishing range of unusual properties, and now Thomas Mattsson and Michael Desjarlais of Sandia National Laboratories in New Mexico have suggested yet another one. They found that water should have a metallic phase at temperatures of 4000 K and pressures of 100 Gpa= about 1 million atmosphere, which are a good deal more accessible than earlier calculations had indicated.

The iron-nickel core as well as the outer mantle may both contain metallic water veins, with the outer core closest to the mantle more conducive to an exotic ionic phase of water.

Until tests can be done with iron and iron-water amalgams at 6000K and 3.6 million atmospheres, we may not know for sure.
« Last Edit: 28/07/2016 12:15:31 by puppypower »
 

Offline evan_au

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Re: What causes Earth's magnetic field?
« Reply #3 on: 28/07/2016 22:48:26 »
Quote from: puppypower
I am not sure, if much work has been done with metallic iron under such extreme conditions to see if the electrons are in higher energy levels, than used for magnetism.
Measurements simulating the core of the Earth can be done in the laboratory using a diamond anvil cell to provide the pressures, and laser beams to provide the temperatures and make measurements of various properties. Magnetic and electrical conductivity can also be tested.

 

Offline AndroidNeox

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Re: What causes Earth's magnetic field?
« Reply #4 on: 29/07/2016 02:05:41 »
So far as I can tell, none of this addresses the problem. Where are the electrical currents? If you don't have net current flow, you don't get magnetic fields. I have not found a single explanation of Earth's magnetic field that addresses the problem of creating an electrical current or producing charge separation across some moving boundary.

Without electrical currents there are no magnetic fields.
 

Offline puppypower

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Re: What causes Earth's magnetic field?
« Reply #5 on: 29/07/2016 12:31:33 »
An interesting discovery, from about 10 years ago, was the earth's core rotates faster than the rest of the planet. For this to be possible, the core will need an engine, that is strong enough to overcome the viscoelastic friction between itself and the outer core. That engine would then generate heat and currents for the magnetic field. It will also be expected to form eddies in the outer core.

http://phys.org/news/2011-02-earth-core-rotating-faster-rest.html

Iron in the presence of water, especially with oxygen, ions and acids, will corrode to form iron oxide with the release of electrons. Natural magnets are often made of lodestone; iron oxide. An electron flow, from the core,  to the surface, appears to be reflected in the oceans of the earth being slightly alkaline or having a slight negative charge; excess electrons in the ocean water.   

The most logical potential needed for core corrosion would be the sun. The sun evaporates surface water. During thunderstorms the clouds build up positive charge. Lightning reflects electrons from the earth meeting the positive charge in the air. The solar evaporation sets a potential for electron flow upward. Since the equator is place of maximum heating and evaporation of water, this would be the place of highest currents. The magnetic field associated with the equatorial currents, will move perpendicular; pole to pole.

This circuit is all dependent on a continuity of water from the atmosphere into the core. This continuity is possible due to process which brought water to the earth, when the earth was forming. Constant asteroid bombardment, especially large ones like the one that formed the moon, would place and trap water throughout the earth.

But even that aside, as temperature and pressure increases, water becomes an increasingly aggressive solvent for minerals. The net result is entropy would drive water diffusion toward the core, once trapped inside and below the crust. While phases of water like super ionic, ion and metallic water, fro mantle to core provide a way to conduct electrons toward the surface.

It was also discovered that the earth is denser north-south compared to east and west. This can be explained with more metallic water east-west, since metallic water, will take up space, but is less dense than most of the mineral phases. Less metallic water north and south would make the earth  denser north-south.
 

Offline evan_au

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Re: What causes Earth's magnetic field?
« Reply #6 on: 29/07/2016 12:33:55 »
Quote from: AndroidNeox
Where are the electrical currents?
They are thought to pass through the conductive metal of Earth's core. They don't have to have a net current flow - in theory the current can flow in circles, if there is some energy source driving it.

The problem is how to start these currents - you need a magnetic field moving relative to the metal to cause a current which produces a magnetic field which damps small-scale turbulence, etc.

Studies of earthquake wave propagation through Earth's inner core suggest that it is rotating at a different rate than Earth's crust. Some laboratory experiments are trying to simulate this effect by having a ball within a ball, rotating at different speeds. 

There is no doubt that this is a difficult question to answer - this is a problem in magnetohydrodynamics, which is even harder to simulate on a computer than the weather.

See: https://www.sciencenews.org/article/spinning-core
The latest experiment: http://complex.umd.edu/research/MHD_dynamos/3m.php

Oops - overlap with puppypower...
 

Offline puppypower

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Re: What causes Earth's magnetic field?
« Reply #7 on: 30/07/2016 12:14:18 »
My theory is energy for the rotation of the core comes from an oxidation of the iron core. The oxidation; rusting, is releasing electrons from the iron core's surface, which drives the core engine, with the currents setting up the magnetic field. The oxidation, in turn, is being induced by solar evaporation which makes the atmosphere positive via water. This potential is conducted to the core, via a continuity of water from the atmosphere to the core. This solar induction is directional; maximized where the sun is overhead. 

A secondary induction from the sun is connected to life and photosynthesis and the production of oxygen O2. Oxygen gas or O2 is electron deficient relative to the iron core. The oxygen in the atmosphere acts like a large non directional electro-positive halo in the atmosphere. There is also a continuity of oxygen from the atmosphere, into the oceans, all the way to the core; from O2 to oxides. The continuity of water and oxygen to the core; as oxides, in the presence of other minerals oxides, at extreme pressure and temperature, puts the hydrogen protons of water into play; acid. This helps corrosion and conduction to the surface. The net affect is a solar powered dynamo.
 

Offline evan_au

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Re: What causes Earth's magnetic field?
« Reply #8 on: 31/07/2016 04:48:13 »
Quote from: puppypower
The oxidation; rusting, is releasing electrons from the iron core's surface, which drives the core engine, with the currents setting up the magnetic field. The oxidation, in turn...
It is thought that the core of the Earth is very much like the iron meteorites that strike Earth from time to time.
https://en.wikipedia.org/wiki/Iron_meteorite

These are composed mainly of a nickel-iron-cobalt alloy, which crystallised over a large period of time (judging by the size of the crystals in the Widmanstätten pattern).
There is not nearly enough water (or other sources of oxygen) to oxidise the core of the Earth. In fact most oxygen bearing compounds are in less-dense layers comprising silica, the oceans & icecaps and the atmosphere.

A theory that seems more in line with these observations is that liquid metal is crystallizing, and these solid crystals are "snowing" down on the core. The heat released by this crystallization is driving the convection currents that generate the Earth's magnetic field.

Currents of water are a much less likely origin of Earth's magnetic field than convection currents in liquid metal.
See: https://en.wikipedia.org/wiki/Inner_core#Dynamics
 

Offline puppypower

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Re: What causes Earth's magnetic field?
« Reply #9 on: 31/07/2016 16:41:26 »
We don't really know enough about the properties of materials at the temperature and pressure of the core of the earth. For example, in one study they found that up to 9.9 wt% of Silicon will dissolve in iron at 130 GPa and 2,600 K. This temperature is way below the 6000K in the core. If you had asteroids of iron sinking in the mantle they will accumulate silicon, making Silicon part of the core.

http://link.springer.com/article/10.1007/s00269-009-0296-0#/page-1

From your second link is this quote :

Quote
...  observations indicating that in fact there is a degree of disorder within the inner core.[17] Seismologists have found that the inner core is not completely uniform, but instead contains large-scale structures such that seismic waves pass more rapidly through some parts of the inner core than through others.[18] In addition, the properties of the inner core's surface vary from place to place across distances as small as 1 km. This variation is surprising, since lateral temperature variations along the inner-core boundary are known to be extremely small (this conclusion is confidently constrained by magnetic field observations).

Recent discoveries suggest that the solid inner core itself is composed of layers, separated by a transition zone about 250 to 400 km thick.[19] If the inner core grows by small frozen sediments falling onto its surface, then some liquid can also be trapped in the pore spaces and some of this residual fluid may still persist to some small degree in much of its interior.

This suggest to me that there are different material compositions, with the layers and lateral materials of the core like a phase diagram. As it cools, different compositions will become solid. That also means the magnetic field should change with cooling due to the changing compositions and crystal structures that are forming.

There is an electrochemical potential between the oxygen in the atmosphere and metallic iron in the core, no matter what phases the iron is part of. The oceans are slightly alkaline; slight negative charge, suggesting electron flow.
« Last Edit: 31/07/2016 16:44:14 by puppypower »
 

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Re: What causes Earth's magnetic field?
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