Do you have any reference that refers to them as "bound"? That don't seem right to me.

All you need to look for are cases where Gauss's Law of magnetism applies. This is usually treated macroscopically for the Faraday disk generator at the core of the Earth, but if it is treated microscopically as above you're going to have your finite elements exhibit a dipole moments. See pages 90-91. Note that although later this goes on to talk about geomagnetization, the mineral approximation must be correct even up beyond the curie point. This is why we have success with finite element analysis.

Currents are all necessarily bound, by the way. Though a macroscopic current can be mapped, the paramagnetism of iron acorrding to Barnett is a major player in how the magnetohydrodynamics can play out.

I'm sorry, I didn't say what resource I was referring to:

http://www-gpsg.mit.edu/12.201_12.501/BOOK/chapter3.pdf

core is under tremendous pressure due to gravity ( 3 500 000 atmospheres ? ). it must heat up and molten. unless our laws of physics don't work at these xtreme prssures ?? ....

At those pressures, the molocules are crammed so close together it is a solid.

I [i]think[/] that it also crystalizes due to the extreme pressure...

__________________
"Light thinks it travels faster than anything but it is wrong. No matter how fast light travels it finds the darkness has always got there first, and is waiting for it." — Terry Pratchett, Reaper Man

441!!!! :)

darkhunter nailed it.

Check out phase diagrams, cable. Temperature and pressure are both important to determine what the phase of matter is going to be. In the case of the core, it was long assumed that the inner core would be solid because the heat probably wouldn't be great enough. This has been confirmed with seismic measurements of intense earthquakes. The inner core happens to be solid.

u rely on sismics ONLY. we only know about some kms under earth surface. you r xtrapolating for a core at xtreme pressure.

I've read recently in a paper about a theory thet fission reaction is taking place in the core, involving uranium. and charged particles resulting from fission are causing the earth mag field. ( sorry can' find it on the web ).

could this radioactive core make sismics looks like if it's solid ??

and if core is solid, how could u xplain reverse mag polarity found in fossiles ??

__________________
"Light thinks it travels faster than anything but it is wrong. No matter how fast light travels it finds the darkness has always got there first, and is waiting for it." — Terry Pratchett, Reaper Man

441!!!! :)

The migration to a new host cut me off. My old browser could no longer see the pages. It took me a while to get a new one, Netscape 7 from Sun. So here I am again! Excuse me if I don't plow through the few pages already up before posting.

The alleged problems put forth, concerning whether or not the Earth's magnetic field has reversed are minor details, none actually relevant to the question. The evidence is overwhelming, and I direct the readers attention, for instance, to the books Reversals of the Earth's Magnetic Field, John A. Jacobs, Cambridge University Press, 1994, and The Magnetic Field of the Earth, R.T. Merrill, M.W. McElhinny & P.L. McFadden, Academic Press, 1996. These two books, especially the former, describe in great detail, the observational evidence that leads to the conclusion that Earth's magnetic field has reversed its polarity numerous times. And, since we have observed the reverse in polarity of the sun's magnetic field, it can hardly be argued that thre is any fundamental problem with the idea of spontaneous field reversal.

I saw a reference somewhere to the Faraday disc model & reversals. That model has not been relevant to the discussion for decades. It has already been nearly 8 years, since the first succesful, physically realistic simulations of geomagnetic field reversals were accomplished (A 3-dimensional self consistent computer simulation of a geomagnetic field reversal, G.A. Glatzmaier & P.H. Roberts, Nature 377(6546): 203-209, September 21, 1995; A 3-dimensional convective dynamo solution with rotating and finitely conducting inner core and mantle, G.A. Glatzmaier & P.H. Roberts, Physics of the Earth and Planetary Interiors 91(1-3): 63-75, September, 1995. Since then these papers have garnered a few hundred citations, and numerous followup studies & simulatiuons have been performed. There are now two extensive review papers on geodynamo simulations, Geodynamo theory and simulations, P.H. Roberts & G.A. Glatzmaier, Reviews of Modern Physics 72 (4): 1081-1123, October 2000; Geodynamo simulations - How realistic are they?, G.A. Glatzmaier, Annual Review of Earth and Planetary Sciences 30: 237-257, 2002. Why is it that creationists never read the books and never read the journal articles, and never know anything about the relevant physics, but are still happy to proclaim things to be impossible, even after they have already happened?

The earth's magnetic field is generated by dynamo action in the fluid outer core, mitigated by the conductivity & rotation of the solid inner core. The basic physics is well established, well understood, and hardly arguable. Barnes' argument is easily refuted, as I have already done, and has already been referenced, but I'll do it again anyaway: On Creation Science and the Alleged Decay of the Earth's Magnetic Field. In fact, his argument is so bad, that creationist D. Russell Humphreys has created an alternative model that includes field reversals, but compresses the time scale to a creationistic 10,000 years. He has problems too, but not quite as severe as barnes did (Humphreys also uses dynamo theory, but his own version, since the real one won't give short enough time scales).

Cheers.

Edited to add links for a couple of papers.

There's a lot there, but I still don't see it. Pages 90-91 are talking about permanent magnetism in surface rocks, not magnetism in the core per se. Are those Brad Hager's notes?
Do you mean all currents in the core? Or do you mean all currents? "Bound" seems to take on a different meaning.
Probably the same reason that Glatzmaier makes claims about successfully modeling the convection of the mantle, but buries a disclaimer within the article that they had to set mantle viscosity in their models to a value one or two orders of magnitude smaller than what it surely is. Everybody pushes their agenda. Let's stick to facts.

We are relying on seismics and pressure arguments. That's two different things. Plus Glatzmaier has a working model:

http://www.es.ucsc.edu/~glatz/geodynamo.html

Fission is not likely to change the density of the core, so it would be hard to argue for a false indicator.

Try Glatzmaier on for size.

Actually, they're more general than that. They can be easily applied to surface rocks because of domain physics being well understood in paramagnetic solids, but it applies to any paramagnetic material (including liquids). After all, Faraday induction occurs as you travel to the Curie point, it doesn't just "turn on" there.


Do you mean all currents in the core? Or do you mean all currents? [/quote]

Currents in the core. The reason for this is because there is no battery.

In some ways, you're right, since we have MHD to deal with, we can have transfer of charge through macroscopic processes.

The BA's take on this (down towards the bottom): The Core review

__________________
"Light thinks it travels faster than anything but it is wrong. No matter how fast light travels it finds the darkness has always got there first, and is waiting for it." — Terry Pratchett, Reaper Man

441!!!! :)

So what's a "transplanet?" Is that an astronomy term I'm not familiar with?

__________________
Everything I need to know I learned through Googling.

"no one has been able to detect a dipole moment"

Am I missing the obvious here? We're getting a moment easily enough, so by my interpretation Yul is suggesting a magnetic monopole. At which point I'll be bowing down before the Lord Himself, if its true.

Facts indeed. And where exactly did Glatzmaier claim that he successfully modeled the convection of the mantle? Anyway, it's not the mantle viscosity, it's the fluid outer core viscosity, and it's not set too low, it's set too high.

The viscosity is set too high, not because of anybody's agenda, but because of their computers. The spatial resolution of the model is tied to the viscosity, because of diffusive eddys. There was not then, and is not now, sufficient computational power available to handle the high spatial resolution required. So the viscosity is set too high, with the result that the model becomes insensitive to small scale, high frequency features. But it does not appear to alter the large scale structure & behavior of the model. This is explained in detail in their paper A 3-dimensional convective dynamo solution with rotating and finitely conducting inner core and mantle, G.A. Glatzmaier & P.H. Roberts, Physics of the Earth and Planetary Interiors 91(1-3): 63-75, September, 1995, and even more so in Glatzmaier's review paper Geodynamo simulations - How realistic are they?, G.A. Glatzmaier, Annual Review of Earth and Planetary Sciences 30: 237-257, 2002.

In fact, if you read the latter review paper, you will find that there is a small list of approximations. In fact, Glatzmaier says "Although the term geodynamo model is used here to refer to spherical dynamo models currently being run as simple analogues of the geodynamo, no one has yet been able to simulate a really 'Earth like' geodynamo, because of the huge computing resources that are required."

But how does this prevent the models from being "physically reasonable", as I asserted (and continue to assert) that they are? I never said it was a truy "Earth like" simulation, and in fact, neither do Glatzmaier & Roberts. But they do assert that the models, including reversals, are physically reasonable. The assertion stands on the ground that the parameter space used for the simulations, while not exatcly Earth like, is certainly close to Earth like, which implies that the structure and behavior of the model should be close to Earth like as well. Even if this turns out in the future to be wrong, it can hardly be criticised as "unreasonable".

Not just him. I googled on glatzmaier viscosity convection mantle and the first thing that came up was this paper. But I see that they make similar disclaimers in the article you mention.
Yep, so why should we say that these simulations are reliable, yet?
The limitations aren't just computational. They've tried other values, but the results don't match reality. Is the reason for that just computational, or is it because they're missing something in the model? We don't know yet.
Well, the argument would go something like this: tectonic plates move about on the surface of the earth at a certain speed that is determined from geological study. When we use our mantle convection model, we do get motion at the surface that simulates what we observe--but in order to do that we have to use viscosity parameters that are one or two orders of magnitude off. Have we "successfully" modeled tectonics then? Yeh, to read the literature. But no not really. We're missing something crucial--in the case of mantle convection, just solving the computational problems is probably not going to mean that the solutions that are produced are going to somehow stay the same, even though we eventually increase the parameters.

Do you have a citation for someone using the term "bound currents" in this fashion?

Grapes ==

Try Jackson's E&M. I don't have my copy here, but the stuff on the forms of permanent magnetism I remember distinctly addressed that issue. Perhaps Zathras will come by with a citation. Otherwise, I encourage you to check it out.

No problem. But this is citation tag--you can't ask anyone else for a citation until you provide this one.

Do you no longer have any objection to Yul's comment about liquid currents, then?

The "liquid currents" advocated by Yul are an oversimplification and a misrepresentation of MHD as far as I can tell. So yes, I stand by my critique of the issue that he says there is nothing that powers them.

In terms of your backhanded criticism of "citation tag", I should point-out that bound currents are a well-understood physical phenomenon and are expressed mathematically in MHD by the point-in-fact of a permanent magnetic moment. This is something you can verify using simple laws of magnetism and electricity. It's proof is in the math, so to speak. Permanent magnetism can only be acheived through a dynamo or through bound currents, but the effect that both produce indistinguishable magnetic fields means that switching back and forth between both definitions is theoretically easy to do. MHD uses both of these approximations, and if one simply reads up on magnetism it is easy to find this out.

So far as I can tell, that is factually incorrect. Mantle convection models use proper viscosities. Plate tectonics models use proper viscosities. See, for instance, The Earth's Mantle, Ian Jackson (editor), Cambridge University Press, 1998, 2000; chapter 6, Plates, Plumes, Mantle Convection, and Mantle Evolution, by Geoffrey F. Davies; chapter 10, The Viscosity of the Mantle; Evidence from Analyses of Glacial-Rebound Phenomena, by Kurt Lambeck & Paul Johnson.. Viscosities are typically 10^20 to 10^21 Pa-S, but the viscosity is not a constant, it depends on pressure, temperature, and geochemistry.

Also note that the page you linked to (3-D Simulations of Mantle Convection and the Earth's True Polar Wander) does not indicate the value(s) of viscosity they use, though as you indicate, they do make the same discalimer as Glatzmaier, namely that they are bound by available computational power. Nowhere do they indicate that "real" viscosities don't work.

Indeed, I cannot find reference to any study which has problems with physically realistic viscosities, as you imply. Feel free to provide such, should you have one.

Well, as even Glatzmaier explicitly says in his Ann. Rev. review, they may not be reliable. But I think they are, and should be considered reliable, because they are simply not far enough away from "real Earth" models to imply a major source of unreliability. I think it's perfectly reasonable to assume that, the closer the model gets to the real thing, the closer it will be to reproducing the behavior of the real thing. And so it has been with these models; the closer they get to "real Earth" in structure, the closer they get to "real Earth" in behavior too. So why should we assume they are not reliable?

It's not that simple, apparently. I haven't been able to find a citation that considers a dynamo "permanent magnetism" in the sense that we're discussing.

It may well be that you're discussing a different sense, but I haven't been able to find a discussion in that sense either.
And why do you call those "proper viscosities?"
What do you suppose isn't working then? Why would Glatzmaier say such things?
The debate has raged within the geophysics community for over thirty years, but the first few years were stealth debate (researchers were coming up with opposing results, but discarding them out of hand). The book Mantle Convection, editted by Peltier, was a monster, and presented a lot of the issues on both sides. The low viscosity side has pretty much lost out since then.
Glatzmaier is one of the world experts on the subject. The model viscosity is over a magnitude off. Just imagine a world where plate tectonic speeds were 2 millimeters per year instead of 2 centimeters. We could swim to Europe.
They've tried to model the real Earth, and they haven't been able to.

There is an intractable problem that all continental drift theories have yet to solve. The stiffness of the mantle that is supposed to be moving the continents is many orders higher than the lowest value that could possibly allow any movement at all. To allow convection, the viscosity assumed by Wegener was 10^16 cgs units, whereas the actual values range from 10^24 to 10^26. His value was 10^8 to 10 too low.

The actual values range from 10^20 through 10^25 Pascal-seconds (Pas). Your values are a tad too large. See, for instance, Mantle Viscosity and the Thickness of the Convective Downwellings, by Uwe Walzer, Roland Hendel, and John Baumgardner. Their figure 3 shows the preferred radial dependence of viscosity in the mantle, according to their model, as high as 10^25, around 2500 km below the surface, and below 10^21 near 250 km, and back to around 5x10^22 near the surface. And I note that co-author John Baumgardner is a committed young Earth creationist.

But their model isn't the last word either. See, for instance, Motion of Hotspots and Changes of the Earth's Rotation Axis Caused by a Convecting Mantle (abstract only), the 1996 PhD thesis of Bernhard Steinberger. He puts the viscosity under Hawaii at roughly 1.5 x 10^20, and says the lower mantle viscosity can't be over about 3.6x10^24, a bit less than the model in the previous paper. And if you reference the chapter 10 from my last message, you will find once again that the mantle viscosities are on the order of 10^20 to 10^21 Pas. Most sources would put the viscosity about an order of magnitude below that of the Walzer, Hendel & Baumgardner study.

So Wegener was wrong.

The continents do move, you know. We can see them move in real time, either by using new-fangled GPS, or the old fashioned way, with VLBI radio astronomy ( Global Tectonics using VLBI, SLR, and GPS or VLBI -- Measuring Our Changing Earth).

Whether the mantle drags the continents along with it, or the continents drag the mantle along with them, remains I think an open issue.

I also note in passing that none of this is relevant to the dynamo generation of Earth's magnetic field.

I suspect that you are both "talking past each other", so to speak. One of the early theories for the genesis of Earth's magnetic field was that that solid core acted like a bar magnet, that the field came from it's own permanent magnetism. That theory fell by the wayside long ago, when it was realized that the solid core is well above its Curie temperature, and can't have its own, permanent magnetic field.

The magnetic field of a permanent magnet comes from the aligned electron spins, where the electrons constitute the current, and their aligned magnetic moments combine to the effect of a macroscopic magnetic field. That alignment is destroyed (and the macroscopic field goes away), if the material gets too hot.

It's all about the property of ferromagnetism.

Because they are the observationally determined values of the mantle viscosity.

Considering that we have already asked & answered this, why are you even asking? We do not know that it "does not work", nor have you presented any evidence to support the assertion. They have not tried, because they don't have the computational power available yet to do so. That's not just a guess, it's the explicit statement of the authors, in both cases you have cited (Glatzmaier & Stevenson). So, do you think they are just fibbing?

What constitutes a '"low" viscosity, accroding to you?

Glatzmaier never even mentioned the mantle viscosity. He was talking about the viscosity of the liquid outer core, which has approximately diddly-squat to do with plate tectonics.The real question you should be asking is how the different viscosity affects the generated magnetic field.

A,nd I will remind you that "viscosity" and "velocity" are not the same thing. Glatzmaier's maximum fluid velocity was 0.4 cm/sec, which would cover a distance of 1 meter in about 4 minutes. That's not an unreasonable velocity. The viscosity that Glatzmaier is interested in, the one he can't handle, is not the kinetic viscosity, its the viscosity of molecular diffusion. It's all there in his paper, the one I have from Physics of the Earth and Planetary Interiors, 1995. It's also in the Rev. Mod. Phys. review paper.

In what sense? There is still quite a bit we don't know about Earth, so whether or not "they" have been able to model it, depends on the criteria that constitute a "good" model. In the case of the geomagnetic field, I would say the models are very good, but of course, they could be better. And I think there is no valid reason to doubt that Earth's magnetic field is generated by a dynamo process.

And finally, I point out that you keep harping on the mantle. It's not relevant. Glatzmaier did not concern himself with the viscosity of the mantle, and it is not largely relevant to geomagnetism. The viscosity that is relevant is that of the liquid outer core.

I don't think so. JS has said that the magnetic field of the Earth is somehow related to permanent magnetism, or bound currents, in some way.
Yes, that seems to disagree with JS.

You gotta admit, observations of mantle viscosity include a lot of assumptions. Some of the original determinations of viscosity were based upon plate tectonic speeds--in other words, what viscosity would you have to have in order for the plates to be entrained and move at the speeds we observe.
The claim I made above, that researchers are reporting success with models, but then within their reports are admissions that they still don't have the compute power to actually model the Earth, is not fibbing, or lies, I think they're being straightforward. But they do claim success in modeling process--yes, we see the magnetic reversals in our model, or yes we see plate tectonic motion in our model--but the models aren't really modeling the Earth regime, they admit. Isn't that a fair assessment, given what we know?

I agree that the models are close (only an order of magnitude off, some people don't realize how much progress that represents), and that there have been tremendous advances made in the field, but the disclaimers are there. The point is, we haven't really been able to do the computations. Is it a limit on compute power? Or is it a problem with the model? You can do the back of the envelop calculation with a pencil, and it comes up an order of magnitude short. That's why the lower mantle viscosity estimates of thirty years ago were a couple of magnitudes higher--in order to satisfy such computations.
In the article I referenced he was. Well, he was talking about Rayleigh number, which is a nondimensional parameter related to viscosity.
He has worked on both problems. My original comment about Glatzmaier was concerning his mantle convection work, but I notice that his disclaimers concerning that work are similar to the disclaimers that he includes with the dynamo work.

I'm not doubting that the Earth's magnetic field is generated by a dynamo. I'm just pointing out that the researchers in the field keep admitting that we're still an order of magnitude away from properly modeling it, whereas a lot of people seem to have the impression that those models have already done so.

Lomnitz's Law says that the amount of creep in rocks under stress is logarithmic with time i.e. with constant stress, the amount of movement decreases with time, giving eventually very little progress at all. This is hardly ever referred to by supporters of the theory, and the Encyclopaedia Britannica gave no entry under his name.
In confirmation, an article in Nature (225:1007) notes:
"Convection demands the elastoviscous law, which is contradicted
by all the available evidence. Similarly, to maintain continental
drift, in any way, at a constant rate would require a steadily
increasing force."
This factor is a most formidable barrier to the orthodox convection theory

That I can agree with.

Not a barrier. Not even particularly important. you didn't find a hit on "Lomnitz's law" because nobody ever called it that except Jeffreys, so far as I can tell. It is better known as "power law creep". Lomnitz was one of many who suggested creep laws for rocks, as Jeffreys points out. Lomnitz based his proposed law on laboratory observations of igneous rocks under stress. But the conditions are too far removed from those of the deep mantle to be relevant. Phases changes under pressure changes the rheology of the rocks, such that mantle magma does not obey "Lomnitz's law". See the book I cited before, The Earth's Mantle, chapter 11, Mantle Rheology: Insights from Laboratory Studies of Deformation and Phase Transition.