New theory suggests magnesium could be the key to understanding Earth's magnetic field

New theory suggests magnesium could be the key to understanding Earth’s magnetic field
Two types of chemical convection in Earth's core. Precipitating a thin layer of magnesium-rich minerals at the top of the core provides as much energy for the magnetic field as forcing silicon and oxygen out of the entire inner core. Credit: Joseph O'Rourke

(Phys.org)—A pair of planetary scientists has come up with a new theory to help explain the mechanism behind the generation of the Earth's magnetic field. In their paper published in the journal Nature, Joseph O'Rourke and David Stevenson, both with the California Institute of Technology, suggest that magnesium that made its way to the core of the planet during its early history could be the key to understanding how the magnetic field was generated in the past and what drives it in the present. Bruce Buffett with the University of California offers a News & Views piece on the work done by the team in the same journal issue.

For many years, scientists have believed that the Earth's is likely generated by energy that is released as the core cools and material solidifies, and radioactive decay—causing churning, the essence of the geodynamo. But, there is a problem with that idea, scientists also believe that the core did not cool enough to form an inner core, until approximately one billion years ago—that begs the questions of what caused the magnetic field to come about before there was sufficient cooling? The research pair with this new effort suggest it has to do with —they propose that it was introduced to the core during the time when the Earth was being formed, by collisions with other protoplanets, approximately 3.4 to 4.2 billion years ago.

They further suggest that magnesium could make up as much as 1 percent of the material in the core, and because magnesium is only soluble in iron at very high temperatures, they believe that it is slowly precipitating out to the boundary between the core and the mantle. That process, the team notes, would leave the iron behind denser, which would cause the release of energy, which they suggest could explain the power source behind the dynamo. Their theory would explain how it is that the magnetic field has been present for so long—it would also suggest that it continues to play at least a part in how the field is generated today—with magnesium possibly driving iron convection from the top part of the core while the release of light elements from the inner would drive convection from the bottom side.

The team used computer models in developing their theory which means experiments will have to be conducted to help bolster their ideas.


Explore further

New study indicates Earth's inner core was formed 1 - 1.5 billion years ago

More information: Joseph G. O'Rourke et al. Powering Earth's dynamo with magnesium precipitation from the core, Nature (2016). DOI: 10.1038/nature16495

Abstract
Earth's global magnetic field arises from vigorous convection within the liquid outer core. Palaeomagnetic evidence reveals that the geodynamo has operated for at least 3.4 billion years, which places constraints on Earth's formation and evolution. Available power sources in standard models include compositional convection (driven by the solidifying inner core's expulsion of light elements), thermal convection (from slow cooling), and perhaps heat from the decay of radioactive isotopes. However, recent first-principles calculations and diamond-anvil cell experiments indicate that the thermal conductivity of iron is two or three times larger than typically assumed in these models. This presents a problem: a large increase in the conductive heat flux along the adiabat (due to the higher conductivity of iron) implies that the inner core is young (less than one billion years old), but thermal convection and radiogenic heating alone may not have been able to sustain the geodynamo during earlier epochs. Here we show that the precipitation of magnesium-bearing minerals from the core could have served as an alternative power source. Equilibration at high temperatures in the aftermath of giant impacts allows a small amount of magnesium (one or two weight per cent) to partition into the core while still producing the observed abundances of siderophile elements in the mantle and avoiding an excess of silicon and oxygen in the core. The transport of magnesium as oxide or silicate from the cooling core to underneath the mantle is an order of magnitude more efficient per unit mass as a source of buoyancy than inner-core growth. We therefore conclude that Earth's dynamo would survive throughout geologic time (from at least 3.4 billion years ago to the present) even if core radiogenic heating were minimal and core cooling were slow.

Journal information: Nature

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Jan 21, 2016
The study of the aurora began much the same, with Royal Society scientists like Sydney Chapman insisting that the aurora was generated locally. His arguments won over the geosciences for a half-century, over the objections of Kristian Birkeland, and Lucy Jago (Birkeland's biographer) has suggested in her book on Birkeland that this held the study of the aurora back for a full half-century.

It does not appear that any sort of lesson was learned on the matter, as the approach here is just the same -- completely ignoring the Earth's larger electrodynamic plasma environment.

Jan 21, 2016
"A pair of planetary scientists has come up with a new theory to help explain the mechanism behind the generation of the Earth's magnetic field."

The important thing here is to acknowledge we still don't fully understand how planets and stars generate magnetic fields and what causes them to flip periodically.

Jan 21, 2016
Magnesium.... MAGNETIC field... Duuuh

Jan 21, 2016
"A pair of planetary scientists has come up with a new theory to help explain the mechanism behind the generation of the Earth's magnetic field."

The important thing here is to acknowledge we still don't fully understand how planets and stars generate magnetic fields and what causes them to flip periodically.

It's important to clarify, the mainstream space scientists don't fully, or even partially, understand how any magnetic fields are created. They still believe in frozen-in fields and such. Applied scientists such as EE are well aware electric currents/fields are required for generating magnetic fields. They also understand putting salt water in a blender will not create a magnetic field, in contrast to astrophysicists.
The following paper explains A). How magnetic fields are created, and B) polarity flip in those fields.

It's clear astrophysicists need a refresher course in real EE concepts.

Jan 22, 2016
The paper is paywalled, but it seems the model is independent of when the magnesium was delivered (as long as it was before 3.4 Ga). A robust model.

************

Re magnetism: "we still don't fully understand".

No, but we do understand a lot. That is why it is so curious to see cranks claim stuff that doesn't work, or claim that what is observed and already taught at university level doesn't work. You would think they would try to learn a little about EM processes before they spout.

[tbctd]

Jan 22, 2016
E.g. to say that frozen-in fields doesn't exist is like claiming neon lights (plasmas) doesn't exist. Or to claim that salt water doesn't generate currents that in turn generate magnetic fields is the same; geophysicists join the astrophysicists in not obeying crank 'physics':

"a magnetometer lowered by a cable from a ship can be used to determine vertical profiles of the ocean velocity ... Figure 1: Predicted amplitude of the vertical component of the magnetic field at the Earth's surface generated by ocean flow due to the lunar M2 tide. Reproduced from Kuvshinov and Olsen (2005b)."

[ http://farside.ph...e62.html ; http://geomag.org...cycl.pdf ]

I am amused that cranks never have references, just claims of having them. Just like they claim to have "science", but no real science is ever seen. =D =D =D

Jan 23, 2016
bschott, I think you are on the wrong thread, I don't see the commenter you named. May I suggest glasses, to go with the remedial reading (and physics!) you seem to need?

Jan 25, 2016


In this instance, when confronted with this kind of simple physics that refutes a mainstream claim about how something works I often run into people who have no clue how to answer a question directly, who then refer me to their physics curriculum...but since I can answer the question without it destroying the theory I support, why the hell would I have any interest in their curriculum?

One more time: How do you reverse the polarity of a magnetic field that is a product of a current?


I haven't read it in-depth, but I would consult the experimental data:

https://en.wikipe...l#Causes

Jan 26, 2016
@bschott: If you can't ask nicely, don't.

@anonym: Nice find, since the simulations show what the cranks says is impossible. Of course the already given EM theory is simpler, to reverse a B field you reverse the E field change. (Say, run the current in the reverse direction through an electromagnet. Don't we all do that in school? I know I did.)

Jan 26, 2016
* I suppose I could have given a nod to Wikipedia *

You could link to external valid references cited in Wikipedia but to suggest that Wikipedia articles have any authority is um ..

( Activates ad hominem restraint systems )

... not good practice.

Jan 26, 2016
Note the last sentence of the section I linked to. It refers to an EXPERIMENT rather than just a simulation.

Jan 26, 2016
The actual experiment is reported here:

http://arxiv.org/...1076.pdf

I'm not sure what you linked to. The flow of the sodium was caused by the impellers. However, they observed field reversals despite not reversing the direction of the impellers.

To discredit dynamo theory, you would have to demonstrate the lack of a rotating, convective, conductive fluid in the core, no?

Jan 26, 2016
Hello everyone,
I have read your comments regarding this article and would like to say that I believe I can answer most of your questions regarding the Earth's magnetic field. I am a researchers with over 20 years of studying Earth's magnetic field, but I am not a scientist. Therefore you are not going to get a lot of technical terms and complex explanations from me. I can answer questions about how the field is maintained, where the dynamo system is located, what energy source powers the dynamo system, how earth's magnetic field is related to the magnetic fields of other planets, why the magnetic pole is tilted away from the geographic north pole and so on. However, I cannot tell you why the reversals take place. Perhaps we can figure that out together. If you have a question,keep it simple. I will answer one question at a time.

Jan 28, 2016


Hi Rojack, why does venus not have a magnetic field?



Venus does not have a magnetic field because the magnetosphere is inadequate. Basically, it to weak to produce a strong magnetic field. There are no belts of trapped radiation such as Earth's Van Allen belts, and there is no 'magnetotail' composed of fields of planetary origin.

Jan 28, 2016
"Hi Rojack, why does venus not have a magnetic field?"

Venus does not have a magnetic field because the magnetosphere is inadequate. Basically, it to weak to produce a strong magnetic field. There are no belts of trapped radiation such as Earth's Van Allen belts, and there is no 'magnetotail' composed of fields of planetary origin.

Jan 29, 2016
It does not appear that any sort of lesson was learned on the matter, as the approach here is just the same -- completely ignoring the Earth's larger electrodynamic plasma environment.


plasmasrevenge,
You seem to think that Earth's magnetic field has something to do with "Earth's larger electrodynamic plasma environment" and I believe you are correct. I wold like to discuss what I call the bigger picture. The bigger picture is that planet earth is a small but very important component of the system that creates, maintains, and supplies fuel for the dynamo. The magnetosphere houses the dynamo and its fuel comes from the sun. The magnetic axis is the center of the system, not the planet. The center of the magnetic axis is the strongest part of the magnetic field because that is where all the lines of force come together. The iron core of planet earth is drawn to the center of the magnetic axis. In other words, the magnetic axis is generated by the dynamo system.

Feb 02, 2016
Are the commenters here aware of the detailed GRACE mapping of the fluctuating gravity 'field' which matches precisely the planet wide active tectonics sectors where 5+ mag. earthquakes and much volcanic activity occurs? The 'ring of fire' and other areas show close alignment where sharp high to low field 'shear' is present. The pattern is a set of latitudinal bands offset at the equator, high at the north hemisphere matching low in the southern hemisphere. Even Mars gravity satellite data matches the Earths pattern.
I describe that as it may relate to the magnetic field temporal swings as strongly as we see the Earth's plate tectonics controlled by the gravity field. We claim to map tectonics movement by magnetic reversals, yet the magnetic field is not stable, and tectonics may or may not be. The GEOID shows equatorial offset currently, as does the GRACE field mapping.
I have left the intrigue details for commenters here, and can show a visual map of my description if requested.

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